feat(network): pluggable connection filters; file blocklist + contribute-first CrowdSec (#2542)

Reshapes IP banning around one idea: **core owns the question, content owns every answer.**

Core gains a single accept-path seam — `IConnectionFilter` — and loses everything that used to implement one. The firewall moves to UOContent, a new file-backed blocklist joins it there, and CrowdSec is repositioned from an in-app enforcer to a contribute-first reporter.

## The seam

```csharp
public interface IConnectionFilter
{
    string Name { get; }
    void Configure();
    void Start(CancellationToken token);
    void Stop();
    bool ShouldDeny(IPAddress address);
}
```

The accept path went from hardcoded branches to one question:

```csharp
else if (ConnectionFilters.ShouldDeny(remoteIP, out var deniedBy))
{
    logger.Debug("{Address} denied by connection filter '{Filter}'", remoteIP, deniedBy);
}
```

Filters register during the Configure sweep. The registry is a plain array walked by an indexed loop — no enumerator, no closure, no allocation — and the first denial short-circuits. An interface dispatch is noise next to the `accept()` syscall, so pluggability costs nothing measurable on the path that has to survive a DDoS.

Whatever a hit implies — persisting, promoting to an OS bouncer, contributing to the ban channel — is the filter's business, not the accept path's.

A filter that throws is **unregistered and the connection fails open**. A filter that faults once faults for every subsequent connection, so leaving it registered means an exception and a log line per accept — exactly the amplification an attacker wants — and a broken filter must not be able to deny everyone either.

This deliberately does **not** reuse `EventSink.InvokeSocketConnect`: that fires later and allocates a `SocketConnectEventArgs` per connection, which is what the accept path avoids for rejected traffic.

## What ships behind it

**`firewall`** (UOContent) — the existing admin-curated set. Collapsed from `Firewall` + `AdminFirewall` + a threaded enforcer into one single-threaded store with **zero concurrency primitives**: the accept path, admin gump, TTL expiry and boot load all run on the game loop. Persists to `Configuration/firewall.json` with automatic migration from the legacy `firewall.cfg`. No behavior change for operators — same namespace, same gump, same commands.

**`blocklist`** (UOContent) — new. Holds a millions-strong list in-app and **demand-pages** hits up to CrowdSec, which promotes them to the OS firewall.

The motivation is concrete: CrowdSec's Windows bouncer cannot load the ~3.9M IPs that 91 community feeds produce, but it handles ~100k fine. So the millions live in-process behind a binary search, and only addresses that *actually connect* get promoted. A `PromotedGuard` suppresses re-reporting an address until the bouncer picks it up.

The list is parsed straight from UTF-8 file bytes with no per-line string allocation, off the game loop, and published as an immutable snapshot swapped through a single `volatile` reference. Reloads yield to world saves.

**`tools/Export-IpBlocklist.ps1`** — the producer. Requires PowerShell 7 and runs on Windows, Linux and macOS; Windows PowerShell 5.1 is refused up front via `#requires`. Merges a thin, non-overlapping feed set into one de-duplicated, bogon-filtered file. Parsing runs in a compiled `Add-Type` hot loop (~1s for ~4M lines instead of minutes). Written to a `.tmp` sibling and swapped with `File.Replace`, so the shard never reads a half-written list, and a total feed outage refuses to overwrite a good list with an empty one. Re-running is idempotent — it exits without downloading anything while the list on disk is younger than `-MinInterval` (default 2h, the anchor feed's own refresh period), so a misconfigured scheduler can't hammer upstream.

## CrowdSec: contribute-first

`IBanReporter` + `BanChannel` fan locally-decided bans out to external systems. `CrowdSecReporter` (UOContent) posts to LAPI `POST /v1/alerts` and retracts via `DELETE /v1/decisions`.

Reporting is **enqueue-only** on the accept path: a bounded, coalescing channel drained off-loop with bounded retry, counted drops on overflow, and a flush on shutdown. Under a DDoS the accept path never does synchronous or lock-contending per-IP work.

### Why not pull decisions from CrowdSec?

The original design streamed decisions into an in-app snapshot and enforced them at the accept gate. That's the wrong layer: by the time the shard sees the connection, the TCP handshake and socket setup are already paid for. `cs-firewall-bouncer` drops the same traffic **at the kernel**, and it's what CrowdSec is built to do. So the shard now contributes what it uniquely knows (rate-limit trips, blocklist hits from real connection attempts) and lets the OS enforce.

The one thing the OS can't do — hold millions of entries on Windows — is exactly what the in-app blocklist covers, and it feeds the same pipeline.

## Threading policy

`CLAUDE.md` rule #3 is rewritten as an explicit three-part policy, with rule #10 restated in tandem:

- Anything touching game state runs **only** on the main loop.
- Heavy work that *needs* game state must be **chunked** across ticks, never threaded.
- Heavy work that does *not* need game state (large-file parse, external I/O) **must** run off-loop **and must yield to world saves**.

Results come back via an immutable snapshot swapped through a single `volatile` reference, or `Core.LoopContext.Post` — never by letting the scheduler decide where heavy work runs. Both new subsystems follow it.

## Shared primitives

`SortedRangeIndex<T> where T : IBinaryInteger<T>` — coalesced disjoint interval arrays plus a binary search. The firewall, the blocklist, and (as of this PR) core's reserved-network tables all use it.

Coalescing is a correctness requirement, not an optimization: multi-feed lists nest CIDRs (`/24` containing a `/32`), and a search that inspects only the rightmost run whose minimum is ≤ the value is sound **only** over disjoint runs. That bug was caught in review and is covered by regression tests.

`IPAddressUtility` collects the allocation-free `IPAddress` ↔ `UInt128` conversions and CIDR parsing that were previously scattered or duplicated.

## Config

| File | Owner | Keys |
|---|---|---|
| `Configuration/bans.json` | core | `reportRateLimitTrips`, `autoBanDuration` |
| `Configuration/blocklist.json` | content | `file`, `reloadInterval`, `reportHits`, `banDuration`, `promoteSuppression` |
| `Configuration/crowdsec.json` | content | `lapiUrl`, `machineId`, `password`, `origin`, `manualBanDuration`, `flushInterval`, `maxQueue` |
| `Configuration/firewall.json` | content | persisted firewall entries (migrated from `firewall.cfg`) |

Everything is inert by default. CrowdSec self-disables without credentials; the blocklist self-disables until its file exists. A shard that changes nothing sees no behavior change.

## Notes for review

- **Core no longer references `Firewall` or `IFirewallEntry` anywhere.** `NetworkUtilities` used to build its reserved-network tables out of `CidrFirewallEntry`, which coupled core to the firewall for something unrelated to banning; those are now a `SortedRangeIndex<UInt128>`, same semantics and public API.
- **`BanChannel.Stop()` no longer persists the firewall** — a contribution coordinator has no business saving an enforcement store. That's the firewall filter's `Stop()`.
- **A dead `whitelisted` parameter was dropped** from the blocklist gate: it was hardcoded `false` at its only call site, and no whitelist concept exists in core.
- **The blocklist filter is an instance, not a static.** The static version forced its tests onto the sequential collection with a reset hook; they now run in parallel.
- `dev-docs/networking-packets.md` documents the seam for content authors, plus a known wart in the `IPAddress` ↔ `UInt128` normalization flagged for a follow-up PR.
- The generator was verified on Linux, macOS and Windows under a temporary CI matrix (since removed). It caught two portability bugs — a Windows-only path separator, and a culture-sensitive duration parse that read `2.5` as `25` on comma-decimal locales and *silently* turned a 2.5h cooldown into 25h — plus a third that made the script unparseable on Windows PowerShell 5.1. The source is ASCII-only for that last reason: `#requires` is only honored once a file parses, so non-ASCII in a BOM-less script produces parse errors instead of the version message.

## Tests

**1344 pass** (782 `Server.Tests`, 562 `UOContent.Tests`). New coverage: filter registry (registration, short-circuit, fault-disable), blocklist parsing/CIDR/coalescing, snapshot reload markers, promote-guard TTL, ban-channel fan-out, CrowdSec alert building/dedup/flush-on-stop, and the generator's output-format contract pinned against the reader.

Projects/Server.Tests/Fixtures/TestServerInitializer.cs

@@ -1,3 +1,4 @@
+using System;
 using System.IO;
 using System.Reflection;
 using System.Threading;
@@ -78,6 +79,15 @@ internal static class TestServerInitializer
             Core.LoopContext = new EventLoopContext();
             Core.Expansion = Expansion.EJ;
 
+            // Seed the loop clock as Main.cs does before the Configure sweep; otherwise Core.Now is
+            // DateTime.MinValue for the whole test host.
+            Core._now = DateTime.UtcNow;
+
+            // Timer wheel must exist before NetState.Configure(), which schedules a recurring
+            // sweep via Timer.DelayCall (matches production ordering in Main.cs: Timer.Init runs
+            // before AssemblyHandler.Invoke("Configure")).
+            Timer.Init(0);
+
             // Configure networking (initializes RingSocketManager for tests)
             Server.Network.NetState.Configure();
 
@@ -87,8 +97,6 @@ internal static class TestServerInitializer
             // Configure the world
             World.Configure();
 
-            Timer.Init(0);
-
             // Load the world
             World.Load();
 

Projects/Server.Tests/Tests/Network/Bans/BanChannelTests.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans;
+
+public class BanChannelTests
+{
+    private sealed class FakeReporter : IBanReporter
+    {
+        public readonly List<(IPAddress ip, TimeSpan ttl, string reason)> Reports = [];
+        public readonly List<IPAddress> Retractions = [];
+        public bool ThrowOnReport;
+
+        public string Name => "fake";
+        public bool CanRetract => true;
+        public void Register() { }
+        public void Start(CancellationToken token) { }
+        public void Stop() { }
+
+        public void Report(IPAddress address, TimeSpan ttl, string reason)
+        {
+            if (ThrowOnReport)
+            {
+                throw new InvalidOperationException("boom");
+            }
+
+            Reports.Add((address, ttl, reason));
+        }
+
+        public void Retract(IPAddress address) => Retractions.Add(address);
+    }
+
+    [Fact]
+    public void Report_FansOutToAllReporters()
+    {
+        var a = new FakeReporter();
+        var b = new FakeReporter();
+        BanChannel.ConfigureForTesting([a, b]);
+
+        BanChannel.Report(IPAddress.Parse("1.2.3.4"), TimeSpan.FromHours(1), "rate-limit");
+
+        Assert.Single(a.Reports);
+        Assert.Single(b.Reports);
+        Assert.Equal("rate-limit", a.Reports[0].reason);
+    }
+
+    [Fact]
+    public void Report_SwallowsReporterException()
+    {
+        var bad = new FakeReporter { ThrowOnReport = true };
+        var good = new FakeReporter();
+        BanChannel.ConfigureForTesting([bad, good]);
+
+        BanChannel.Report(IPAddress.Parse("1.2.3.4"), TimeSpan.FromHours(1), "manual");
+
+        Assert.Single(good.Reports); // the throwing reporter does not block the others
+    }
+
+    [Fact]
+    public void Retract_ReachesRetractCapableReporters()
+    {
+        var a = new FakeReporter();
+        BanChannel.ConfigureForTesting([a]);
+
+        BanChannel.Retract(IPAddress.Parse("9.9.9.9"));
+
+        Assert.Single(a.Retractions);
+    }
+}

Projects/Server.Tests/Tests/Network/Bans/BanConfigurationTests.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Text.Json;
+using Server.Json;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests;
+
+public class BanConfigurationTests
+{
+    // Locks the JsonConfig casing/converter contract: JsonConfig's options are case-SENSITIVE, so
+    // every settings member must carry an explicit [JsonPropertyName("camelCase")] or it silently
+    // binds nothing. These tests round-trip through the exact options the loader uses.
+
+    [Fact]
+    public void BanSettings_RoundTripsThroughJsonConfig()
+    {
+        var original = new BanSettings
+        {
+            ReportRateLimitTrips = false,
+            AutoBanDuration = TimeSpan.FromHours(2)
+        };
+
+        var json = JsonConfig.Serialize(original);
+
+        Assert.Contains("\"reportRateLimitTrips\"", json);
+        Assert.Contains("\"autoBanDuration\"", json);
+
+        var restored = JsonSerializer.Deserialize<BanSettings>(json, JsonConfig.DefaultOptions);
+
+        Assert.NotNull(restored);
+        Assert.Equal(original.ReportRateLimitTrips, restored.ReportRateLimitTrips);
+        Assert.Equal(original.AutoBanDuration, restored.AutoBanDuration); // TimeSpan survives
+    }
+
+    [Fact]
+    public void BanSettings_Defaults_AreReportRateLimitTripsFourHourAutoBan()
+    {
+        var settings = new BanSettings();
+
+        Assert.True(settings.ReportRateLimitTrips);
+        Assert.Equal(TimeSpan.FromHours(4), settings.AutoBanDuration);
+    }
+}

Projects/Server.Tests/Tests/Network/ConnectionFiltersTests.cs

@@ -0,0 +1,133 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: ConnectionFiltersTests.cs                                       *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Net;
+using System.Threading;
+using Server.Network;
+using Xunit;
+
+namespace Server.Tests.Network;
+
+[Collection("Sequential Server Tests")]
+public class ConnectionFiltersTests : IDisposable
+{
+    public ConnectionFiltersTests() => ConnectionFilters.ResetForTesting();
+
+    public void Dispose() => ConnectionFilters.ResetForTesting();
+
+    [Fact]
+    public void No_filters_denies_nothing()
+    {
+        Assert.False(ConnectionFilters.ShouldDeny(IPAddress.Parse("1.2.3.4"), out var deniedBy));
+        Assert.Null(deniedBy);
+    }
+
+    [Fact]
+    public void Register_is_idempotent_by_name()
+    {
+        ConnectionFilters.Register(new FakeFilter("dupe", deny: false));
+        ConnectionFilters.Register(new FakeFilter("dupe", deny: true));
+
+        // The second registration is ignored, so the deny:true instance never gets consulted.
+        Assert.Single(ConnectionFilters.Filters);
+        Assert.False(ConnectionFilters.ShouldDeny(IPAddress.Parse("1.2.3.4"), out _));
+    }
+
+    [Fact]
+    public void First_denying_filter_short_circuits_and_is_named()
+    {
+        var first = new FakeFilter("allow-all", deny: false);
+        var second = new FakeFilter("deny-all", deny: true);
+        var third = new FakeFilter("never-reached", deny: true);
+
+        ConnectionFilters.Register(first);
+        ConnectionFilters.Register(second);
+        ConnectionFilters.Register(third);
+
+        Assert.True(ConnectionFilters.ShouldDeny(IPAddress.Parse("1.2.3.4"), out var deniedBy));
+        Assert.Equal("deny-all", deniedBy);
+        Assert.Equal(1, first.Calls);
+        Assert.Equal(1, second.Calls);
+        Assert.Equal(0, third.Calls); // short-circuited
+    }
+
+    // A filter that throws once throws for every subsequent connection, which would turn one bug into an
+    // exception per accept. It must be dropped, and the connection must fail open rather than be denied
+    // by a filter that never actually answered.
+    [Fact]
+    public void Throwing_filter_is_unregistered_and_fails_open()
+    {
+        var bad = new FakeFilter("bad", deny: true, throws: true);
+        var good = new FakeFilter("good", deny: false);
+
+        ConnectionFilters.Register(bad);
+        ConnectionFilters.Register(good);
+
+        Assert.False(ConnectionFilters.ShouldDeny(IPAddress.Parse("1.2.3.4"), out _));
+        Assert.Single(ConnectionFilters.Filters);
+        Assert.Equal("good", ConnectionFilters.Filters[0].Name);
+
+        // Remaining filters still run on the same pass the faulty one was dropped in.
+        Assert.Equal(1, good.Calls);
+    }
+
+    [Fact]
+    public void Register_configures_immediately()
+    {
+        var filter = new FakeFilter("cfg", deny: false);
+        ConnectionFilters.Register(filter);
+
+        Assert.True(filter.Configured);
+    }
+
+    private sealed class FakeFilter : IConnectionFilter
+    {
+        private readonly bool _deny;
+        private readonly bool _throws;
+
+        public FakeFilter(string name, bool deny, bool throws = false)
+        {
+            Name = name;
+            _deny = deny;
+            _throws = throws;
+        }
+
+        public string Name { get; }
+        public int Calls { get; private set; }
+        public bool Configured { get; private set; }
+
+        public void Register() => Configured = true;
+
+        public void Start(CancellationToken token)
+        {
+        }
+
+        public void Stop()
+        {
+        }
+
+        public bool ShouldDeny(IPAddress address)
+        {
+            Calls++;
+            if (_throws)
+            {
+                throw new InvalidOperationException("simulated filter bug");
+            }
+
+            return _deny;
+        }
+    }
+}

Projects/Server.Tests/Tests/Network/Firewall/FirewallTests.cs

@@ -1,137 +0,0 @@
-
-using System.Net;
-using System.Threading.Tasks;
-using Server.Network;
-using Xunit;
-
-namespace Server.Tests;
-
-public class FirewallTests
-{
-    [Fact]
-    public void Firewall_BlocksIPAddress_WhenAdded()
-    {
-        var ip = IPAddress.Parse("192.168.1.1");
-        var entry = new SingleIpFirewallEntry("192.168.1.1");
-
-        Assert.False(Firewall.IsBlocked(ip));
-
-        Firewall.Add(entry);
-
-        Assert.True(Firewall.IsBlocked(ip));
-    }
-
-    [Fact]
-    public void Firewall_DoesNotBlockIPAddress_WhenNotAdded()
-    {
-        var ip = IPAddress.Parse("192.168.1.2");
-        Assert.False(Firewall.IsBlocked(ip));
-    }
-
-    [Fact]
-    public void Firewall_StopsBlockingIPAddress_WhenRemoved()
-    {
-        var ip = IPAddress.Parse("192.168.1.3");
-        var entry = new SingleIpFirewallEntry("192.168.1.3");
-
-        Firewall.Add(entry);
-        Assert.True(Firewall.IsBlocked(ip));
-
-        Firewall.Remove(entry);
-        Assert.False(Firewall.IsBlocked(ip));
-    }
-
-    [Fact]
-    public void Firewall_BlocksIPRange()
-    {
-        var entry = new CidrFirewallEntry(IPAddress.Parse("10.0.0.1"), IPAddress.Parse("10.0.0.5"));
-
-        Firewall.Add(entry);
-
-        Assert.True(Firewall.IsBlocked(IPAddress.Parse("10.0.0.1")));
-        Assert.True(Firewall.IsBlocked(IPAddress.Parse("10.0.0.3")));
-        Assert.True(Firewall.IsBlocked(IPAddress.Parse("10.0.0.5")));
-
-        Assert.False(Firewall.IsBlocked(IPAddress.Parse("10.0.0.6")));
-    }
-
-    [Fact]
-    public void Firewall_CacheInvalidation_WorksOnUpdate()
-    {
-        var ip = IPAddress.Parse("192.168.1.10");
-        var entry = new SingleIpFirewallEntry("192.168.1.10");
-
-        Firewall.Add(entry);
-        Assert.True(Firewall.IsBlocked(ip));
-
-        Firewall.Remove(entry);
-        Assert.False(Firewall.IsBlocked(ip));
-    }
-
-    [Fact]
-    public void Firewall_ReadsFirewallSetCorrectly()
-    {
-        var entry = new SingleIpFirewallEntry("172.16.0.1");
-        Firewall.Add(entry);
-
-        var found = false;
-        Firewall.ReadFirewallSet(set =>
-        {
-            found = set.Contains(entry);
-        });
-
-        Assert.True(found);
-    }
-
-    [Fact]
-    public void Firewall_IsThreadSafe()
-    {
-        var testIps = new IPAddress[256];
-        for (var i = 0; i <= 255; i++)
-        {
-            testIps[i] = IPAddress.Parse($"192.168.0.{i}");
-        }
-
-        var entry = new CidrFirewallEntry(IPAddress.Parse("192.168.0.1"), IPAddress.Parse("192.168.0.255"));
-        Firewall.Add(entry);
-
-        Parallel.ForEach(testIps, ip =>
-        {
-            var shouldBlock = int.Parse(ip.ToString().Split('.')[3]) is > 0;
-            Assert.Equal(shouldBlock, Firewall.IsBlocked(ip));
-        });
-
-        Firewall.Remove(entry);
-
-        Parallel.ForEach(testIps, ip =>
-        {
-            Assert.False(Firewall.IsBlocked(ip));
-        });
-    }
-
-    [Fact]
-    public void Firewall_DoesNotThrowWhenRemovingNonExistentEntry()
-    {
-        var entry = new SingleIpFirewallEntry("203.0.113.5");
-        Assert.False(Firewall.Remove(entry));
-    }
-
-    [Fact]
-    public void Firewall_CacheHandlesMultipleUpdates()
-    {
-        var ip = IPAddress.Parse("192.168.1.20");
-        var entry = new SingleIpFirewallEntry("192.168.1.20");
-
-        Firewall.Add(entry);
-        Assert.True(Firewall.IsBlocked(ip));
-
-        Firewall.Remove(entry);
-        Assert.False(Firewall.IsBlocked(ip));
-
-        Firewall.Add(entry);
-        Assert.True(Firewall.IsBlocked(ip));
-
-        Firewall.Remove(entry);
-        Assert.False(Firewall.IsBlocked(ip));
-    }
-}

Projects/Server/Collections/SortedRangeIndex.cs

@@ -0,0 +1,134 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: SortedRangeIndex.cs                                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Numerics;
+
+namespace Server.Collections;
+
+/// <summary>
+/// Immutable, allocation-lean membership index over a set of inclusive integer ranges. Ranges are
+/// stored as two parallel arrays (<c>_mins</c>/<c>_maxs</c>) sorted by minimum and coalesced into
+/// disjoint runs, so a single binary search decides membership. Coalescing is required for
+/// correctness: <see cref="Contains"/> only inspects the rightmost run whose minimum is &lt;= the
+/// value, which is only sound when the runs never overlap or nest.
+/// </summary>
+public sealed class SortedRangeIndex<T> where T : IBinaryInteger<T>
+{
+    public static readonly SortedRangeIndex<T> Empty = new([], []);
+
+    /// <summary>An inclusive <c>[Min, Max]</c> range. Singles are represented as <c>Min == Max</c>.</summary>
+    public readonly record struct Range(T Min, T Max);
+
+    /// <summary>Orders ranges ascending by minimum; the coalescing pass in <see cref="Build"/> requires this.</summary>
+    public static readonly Comparison<Range> ByMin = static (a, b) => a.Min.CompareTo(b.Min);
+
+    private readonly T[] _mins;
+    private readonly T[] _maxs;
+
+    private SortedRangeIndex(T[] mins, T[] maxs)
+    {
+        _mins = mins;
+        _maxs = maxs;
+    }
+
+    public int Count => _mins.Length;
+
+    /// <summary>
+    /// True when <paramref name="value"/> falls in any range. Binary-searches for the rightmost run
+    /// whose minimum is &lt;= the value, then tests that value against that run's maximum.
+    /// </summary>
+    public bool Contains(T value)
+    {
+        var lo = 0;
+        var hi = _mins.Length - 1;
+        var found = -1;
+        while (lo <= hi)
+        {
+            var mid = (lo + hi) >> 1;
+            if (_mins[mid] <= value)
+            {
+                found = mid;
+                lo = mid + 1;
+            }
+            else
+            {
+                hi = mid - 1;
+            }
+        }
+
+        return found >= 0 && value <= _maxs[found];
+    }
+
+    /// <summary>
+    /// Builds an index from ranges that are already sorted ascending by <see cref="Range.Min"/> (sort
+    /// the source with <see cref="ByMin"/> first). Overlapping and nested ranges are merged into disjoint
+    /// runs. Two passes over the (pooled) input keep the run count exact so only the two final arrays are
+    /// heap-allocated: pass one counts the runs, pass two fills the exact-size arrays.
+    /// </summary>
+    public static SortedRangeIndex<T> Build(ReadOnlySpan<Range> sortedByMin)
+    {
+        if (sortedByMin.IsEmpty)
+        {
+            return Empty;
+        }
+
+        // Pass 1: count the disjoint runs so the final arrays can be sized exactly.
+        var runs = 1;
+        var curMax = sortedByMin[0].Max;
+        for (var i = 1; i < sortedByMin.Length; i++)
+        {
+            var r = sortedByMin[i];
+            if (r.Min <= curMax)
+            {
+                if (r.Max > curMax)
+                {
+                    curMax = r.Max;
+                }
+            }
+            else
+            {
+                runs++;
+                curMax = r.Max;
+            }
+        }
+
+        // Pass 2: write the coalesced runs into the exact-size final arrays.
+        var mins = new T[runs];
+        var maxs = new T[runs];
+        var w = 0;
+        mins[0] = sortedByMin[0].Min;
+        maxs[0] = sortedByMin[0].Max;
+        for (var i = 1; i < sortedByMin.Length; i++)
+        {
+            var r = sortedByMin[i];
+            if (r.Min <= maxs[w])
+            {
+                if (r.Max > maxs[w])
+                {
+                    maxs[w] = r.Max;
+                }
+            }
+            else
+            {
+                w++;
+                mins[w] = r.Min;
+                maxs[w] = r.Max;
+            }
+        }
+
+        return new SortedRangeIndex<T>(mins, maxs);
+    }
+}

Projects/Server/Main.cs

@@ -1,4 +1,4 @@
-/*************************************************************************
+/*************************************************************************
  * ModernUO                                                              *
  * Copyright 2019-2026 - ModernUO Development Team                       *
  * Email: hi@modernuo.com                                                *
@@ -30,6 +30,7 @@ using Server.Compression;
 using Server.Json;
 using Server.Logging;
 using Server.Network;
+using Server.Network.Bans;
 using Server.Text;
 
 namespace Server;
@@ -260,7 +261,7 @@ public static class Core
                 // ignored
             }
 
-            if (!close && !Core.Headless)
+            if (!close && !Headless)
             {
                 Console.WriteLine("This exception is fatal, press return to exit");
                 ConsoleInputHandler.ReadLine();
@@ -342,6 +343,8 @@ public static class Core
         World.ExitSerializationThreads();
         PingServer.Shutdown();
         NetState.Shutdown();
+        BanChannel.Stop();
+        ConnectionFilters.Stop();
 
         if (!_crashed)
         {
@@ -461,6 +464,8 @@ public static class Core
 
         AssemblyHandler.Invoke("Initialize");
 
+        BanChannel.Start(ClosingTokenSource.Token);
+        ConnectionFilters.Start(ClosingTokenSource.Token);
         NetState.Start();
         PingServer.Start();
         EventSink.InvokeServerStarted();

Projects/Server/Network/Bans/BanChannel.cs

@@ -0,0 +1,143 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BanChannel.cs                                                   *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using Server.Logging;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// Coordinates the configured <see cref="IBanReporter"/> contribution sinks. Enforcement is NOT here —
+/// the accept path asks <see cref="ConnectionFilters"/>. This channel only fans locally-decided bans out
+/// to external systems (CrowdSec), which distribute them to OS-level bouncers.
+/// </summary>
+public static class BanChannel
+{
+    private static readonly ILogger logger = LogFactory.GetLogger(typeof(BanChannel));
+
+    private static IBanReporter[] _reporters = [];
+
+    public static IReadOnlyList<IBanReporter> Reporters => _reporters;
+
+    /// <summary>
+    /// Registers a contribution sink from content (inversion of control). Idempotent by
+    /// <see cref="IBanReporter.Name"/>: a second registration of the same name is ignored. Configures the
+    /// reporter immediately so it is ready before <see cref="Start"/>.
+    /// </summary>
+    public static void Register(IBanReporter reporter)
+    {
+        if (reporter == null)
+        {
+            return;
+        }
+
+        var reporters = _reporters;
+        for (var i = 0; i < reporters.Length; i++)
+        {
+            if (reporters[i].Name == reporter.Name)
+            {
+                return;
+            }
+        }
+
+        reporter.Register();
+
+        var updated = new IBanReporter[_reporters.Length + 1];
+        Array.Copy(_reporters, updated, _reporters.Length);
+        updated[^1] = reporter;
+        _reporters = updated;
+
+        logger.Information("Ban channel registered reporter '{Name}'", reporter.Name);
+    }
+
+    internal static void ConfigureForTesting(IBanReporter[] reporters) => _reporters = reporters ?? [];
+
+    public static void Start(CancellationToken token)
+    {
+        var reporters = _reporters;
+        for (var i = 0; i < reporters.Length; i++)
+        {
+            var reporter = reporters[i];
+            try
+            {
+                reporter.Start(token);
+            }
+            catch (Exception e)
+            {
+                // A broken contribution path must not crash boot — enforcement is local and unaffected.
+                logger.Error(e, "Ban reporter '{Name}' failed to start; continuing without it", reporter.Name);
+            }
+        }
+    }
+
+    public static void Stop()
+    {
+        var reporters = _reporters;
+        for (var i = 0; i < reporters.Length; i++)
+        {
+            var reporter = reporters[i];
+            try
+            {
+                reporter.Stop();
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "Ban reporter '{Name}' threw while stopping", reporter.Name);
+            }
+        }
+    }
+
+    /// <summary>Fans a locally-decided ban out to every reporter. Non-blocking; never throws.</summary>
+    public static void Report(IPAddress ip, TimeSpan ttl, string reason)
+    {
+        var reporters = _reporters;
+        for (var i = 0; i < reporters.Length; i++)
+        {
+            try
+            {
+                reporters[i].Report(ip, ttl, reason);
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "Ban reporter '{Name}' threw during Report", reporters[i].Name);
+            }
+        }
+    }
+
+    /// <summary>Fans a retraction (manual unban) out to every retract-capable reporter.</summary>
+    public static void Retract(IPAddress ip)
+    {
+        var reporters = _reporters;
+        for (var i = 0; i < reporters.Length; i++)
+        {
+            if (!reporters[i].CanRetract)
+            {
+                continue;
+            }
+
+            try
+            {
+                reporters[i].Retract(ip);
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "Ban reporter '{Name}' threw during Retract", reporters[i].Name);
+            }
+        }
+    }
+}

Projects/Server/Network/Bans/BanConfiguration.cs

@@ -0,0 +1,76 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BanConfiguration.cs                                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+using System.Text.Json.Serialization;
+using Server.Json;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// Loads the <see cref="BanSettings"/> from <c>Configuration/bans.json</c> (matching the per-feature
+/// JSON config pattern used by <c>AssistantConfiguration</c>). Loaded once; a missing file writes a
+/// local-only, fail-open template so operators have something to edit.
+/// </summary>
+public static class BanConfiguration
+{
+    private const string _path = "Configuration/bans.json";
+
+    public static BanSettings Settings { get; private set; }
+
+    public static void Configure()
+    {
+        // Idempotent: a second call must not re-deserialize or overwrite an operator's edits.
+        if (Settings != null)
+        {
+            return;
+        }
+
+        var path = Path.Join(Core.BaseDirectory, _path);
+
+        if (File.Exists(path))
+        {
+            Settings = JsonConfig.Deserialize<BanSettings>(path);
+        }
+        else
+        {
+            Settings = new BanSettings
+            {
+                ReportRateLimitTrips = true,
+                AutoBanDuration = TimeSpan.FromHours(4)
+            };
+
+            Save();
+        }
+    }
+
+    private static void Save()
+    {
+        JsonConfig.Serialize(Path.Join(Core.BaseDirectory, _path), Settings);
+    }
+}
+
+/// <summary>Ban-channel policy: which reporters receive contributions, and how auto-detections are handled.</summary>
+public record BanSettings
+{
+    /// <summary>Whether IP rate-limiter trips are contributed to reporters. They never enter the local firewall set.</summary>
+    [JsonPropertyName("reportRateLimitTrips")]
+    public bool ReportRateLimitTrips { get; set; } = true;
+
+    /// <summary>Duration reported for an auto-detected (rate-limit) ban.</summary>
+    [JsonPropertyName("autoBanDuration")]
+    public TimeSpan AutoBanDuration { get; set; } = TimeSpan.FromHours(4);
+}

Projects/Server/Network/Bans/IBanReporter.cs

@@ -0,0 +1,55 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: IBanReporter.cs                                                 *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Net;
+using System.Threading;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// A contribution sink behind <see cref="BanChannel"/>. Reporters receive locally-decided bans
+/// (manual admin bans, rate-limit trips, blocklist promotions) and forward them to an external system
+/// (e.g. CrowdSec), which distributes them to OS-level bouncers. Reporters never answer the accept-path
+/// membership query — that is an <see cref="IConnectionFilter"/>'s job.
+/// </summary>
+public interface IBanReporter
+{
+    /// <summary>Stable id for logging/config (e.g. <c>crowdsec</c>).</summary>
+    string Name { get; }
+
+    /// <summary>Reads configuration. No network or file I/O here.</summary>
+    void Register();
+
+    /// <summary>Starts background delivery. The token is cancelled on shutdown.</summary>
+    void Start(CancellationToken token);
+
+    /// <summary>Flushes and tears down background delivery.</summary>
+    void Stop();
+
+    /// <summary>
+    /// Enqueues a ban contribution. MUST be non-blocking and safe on the accept path: it may only
+    /// enqueue (bounded, drop-on-overflow) and never perform synchronous I/O.
+    /// </summary>
+    /// <param name="ttl"><see cref="TimeSpan.Zero"/> or negative = use the reporter's default duration.</param>
+    /// <param name="reason">Short slug (<c>manual</c>, <c>rate-limit</c>) used as the scenario suffix.</param>
+    void Report(IPAddress address, TimeSpan ttl, string reason);
+
+    /// <summary>True if this reporter can retract a previously-reported ban.</summary>
+    bool CanRetract { get; }
+
+    /// <summary>Enqueues a retraction (e.g. a manual unban). No-op if unsupported.</summary>
+    void Retract(IPAddress address);
+}

Projects/Server/Network/ConnectionFilters.cs

@@ -0,0 +1,155 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: ConnectionFilters.cs                                            *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using Server.Logging;
+
+namespace Server.Network;
+
+/// <summary>
+/// Registry of the <see cref="IConnectionFilter"/> gates the accept path consults, and their lifecycle.
+/// Filters are registered during the Configure sweep and the backing store is a plain array, so
+/// <see cref="ShouldDeny"/> is an indexed loop over a field read — no enumerator, no closure, no
+/// allocation. The whole accept path runs on the game loop, so no synchronization is needed.
+/// </summary>
+public static class ConnectionFilters
+{
+    private static readonly ILogger logger = LogFactory.GetLogger(typeof(ConnectionFilters));
+
+    private static IConnectionFilter[] _filters = [];
+
+    public static IReadOnlyList<IConnectionFilter> Filters => _filters;
+
+    /// <summary>
+    /// Registers a gate (inversion of control, mirroring <c>BanChannel.Register</c>). Idempotent by
+    /// <see cref="IConnectionFilter.Name"/>. Filters are consulted in registration order, so register
+    /// the cheapest and most selective first — core registers the firewall before content is swept.
+    /// </summary>
+    public static void Register(IConnectionFilter filter)
+    {
+        if (filter == null)
+        {
+            return;
+        }
+
+        var filters = _filters;
+        for (var i = 0; i < filters.Length; i++)
+        {
+            if (filters[i].Name == filter.Name)
+            {
+                return;
+            }
+        }
+
+        filter.Register();
+
+        var updated = new IConnectionFilter[_filters.Length + 1];
+        Array.Copy(_filters, updated, _filters.Length);
+        updated[^1] = filter;
+        _filters = updated;
+
+        logger.Information("Registered connection filter '{Name}'", filter.Name);
+    }
+
+    /// <summary>
+    /// True when any filter denies the connection. Short-circuits on the first denial;
+    /// <paramref name="deniedBy"/> names it for logging.
+    /// </summary>
+    public static bool ShouldDeny(IPAddress address, out string deniedBy)
+    {
+        var filters = _filters;
+        for (var i = 0; i < filters.Length; i++)
+        {
+            // A faulty filter must not take down the accept loop for every connection.
+            try
+            {
+                if (filters[i].ShouldDeny(address))
+                {
+                    deniedBy = filters[i].Name;
+                    return true;
+                }
+            }
+            catch (Exception e)
+            {
+                Disable(filters[i], e);
+            }
+        }
+
+        deniedBy = null;
+        return false;
+    }
+
+    /// <summary>
+    /// Drops a filter that threw on the accept path: one that faults once faults for every subsequent
+    /// connection, costing an exception and a log line per accept. Failing open is deliberate — a broken
+    /// filter must not be able to deny every connection either.
+    /// </summary>
+    private static void Disable(IConnectionFilter filter, Exception e)
+    {
+        logger.Error(e, "Connection filter '{Name}' threw on the accept path; unregistering it", filter.Name);
+
+        var filters = _filters;
+        var updated = new List<IConnectionFilter>(filters.Length);
+        for (var i = 0; i < filters.Length; i++)
+        {
+            if (!ReferenceEquals(filters[i], filter))
+            {
+                updated.Add(filters[i]);
+            }
+        }
+
+        _filters = updated.ToArray();
+    }
+
+    public static void Start(CancellationToken token)
+    {
+        var filters = _filters;
+        for (var i = 0; i < filters.Length; i++)
+        {
+            var filter = filters[i];
+            try
+            {
+                filter.Start(token);
+            }
+            catch (Exception e)
+            {
+                // A filter that cannot hydrate must not crash boot; it simply denies nothing.
+                logger.Error(e, "Connection filter '{Name}' failed to start; continuing without it", filter.Name);
+            }
+        }
+    }
+
+    public static void Stop()
+    {
+        var filters = _filters;
+        for (var i = 0; i < filters.Length; i++)
+        {
+            var filter = filters[i];
+            try
+            {
+                filter.Stop();
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "Connection filter '{Name}' threw while stopping", filter.Name);
+            }
+        }
+    }
+
+    internal static void ResetForTesting() => _filters = [];
+}

Projects/Server/Network/Firewall/Firewall.cs

@@ -1,168 +0,0 @@
-/*************************************************************************
- * ModernUO                                                              *
- * Copyright 2019-2026 - ModernUO Development Team                       *
- * Email: hi@modernuo.com                                                *
- * File: Firewall.cs                                                     *
- *                                                                       *
- * This program is free software: you can redistribute it and/or modify  *
- * it under the terms of the GNU General Public License as published by  *
- * the Free Software Foundation, either version 3 of the License, or     *
- * (at your option) any later version.                                   *
- *                                                                       *
- * You should have received a copy of the GNU General Public License     *
- * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
- *************************************************************************/
-
-using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
-using System.Net;
-using System.Runtime.CompilerServices;
-using System.Threading;
-
-namespace Server.Network;
-
-public static class Firewall
-{
-    [ThreadStatic]
-    private static InternalValidationEntry _validationEntry;
-    private static readonly ConcurrentDictionary<IPAddress, int> _isBlockedCache = [];
-    private static readonly ReaderWriterLockSlim _firewallLock = new(LockRecursionPolicy.NoRecursion);
-
-    private static int _firewallVersion;
-    private static readonly SortedSet<IFirewallEntry> _firewallSet = [];
-
-    public static int FirewallSetCount => _firewallSet.Count;
-
-    public static void ReadFirewallSet(Action<IReadOnlySet<IFirewallEntry>> callback)
-    {
-        _firewallLock.EnterReadLock();
-        try
-        {
-            callback(_firewallSet);
-        }
-        finally
-        {
-            _firewallLock.ExitReadLock();
-        }
-    }
-
-    internal static bool IsBlocked(IPAddress address)
-    {
-        if (_isBlockedCache.TryGetValue(address, out var blockVersion) && blockVersion == _firewallVersion)
-        {
-            return true;
-        }
-
-        if (_validationEntry == null)
-        {
-            _validationEntry = new InternalValidationEntry(address);
-        }
-        else
-        {
-            _validationEntry.Address = address;
-        }
-
-        if (CheckBlocked(_validationEntry))
-        {
-            _isBlockedCache[address] = _firewallVersion;
-            return true;
-        }
-
-        return false;
-    }
-
-    private static bool CheckBlocked(IFirewallEntry validationEntry)
-    {
-        if (_firewallSet.Count == 0)
-        {
-            return false;
-        }
-
-        _firewallLock.EnterReadLock();
-        try
-        {
-            var min = _firewallSet.Min;
-            if (validationEntry.CompareTo(min) < 0)
-            {
-                return false;
-            }
-
-            // Get all entries that are lower than our validation entry
-            var view = _firewallSet.GetViewBetween(min, validationEntry);
-
-            // Loop backward since there shouldn't be any entries where the Min address is higher than ours
-            foreach (var firewallEntry in view.Reverse())
-            {
-                if (firewallEntry.IsBlocked(validationEntry.MinIpAddress))
-                {
-                    return true;
-                }
-            }
-
-            return view.Max?.IsBlocked(validationEntry.MinIpAddress) == true;
-        }
-        finally
-        {
-            _firewallLock.ExitReadLock();
-        }
-    }
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool Add(IFirewallEntry firewallEntry)
-    {
-        _firewallLock.EnterWriteLock();
-        try
-        {
-            if (_firewallSet.Add(firewallEntry))
-            {
-                Interlocked.Increment(ref _firewallVersion); // Update version
-                return true;
-            }
-            return false;
-        }
-        finally
-        {
-            _firewallLock.ExitWriteLock();
-        }
-    }
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool Remove(IFirewallEntry entry)
-    {
-        if (entry == null)
-        {
-            return false;
-        }
-
-        _firewallLock.EnterWriteLock();
-        try
-        {
-            if (_firewallSet.Remove(entry))
-            {
-                Interlocked.Increment(ref _firewallVersion); // Update version
-                return true;
-            }
-            return false;
-        }
-        finally
-        {
-            _firewallLock.ExitWriteLock();
-        }
-    }
-
-    private class InternalValidationEntry : BaseFirewallEntry
-    {
-        private UInt128 _address;
-
-        public IPAddress Address
-        {
-            set => _address = value.ToUInt128();
-        }
-
-        public override UInt128 MinIpAddress => _address;
-        public override UInt128 MaxIpAddress => _address;
-
-        public InternalValidationEntry(IPAddress ipAddress) => Address = ipAddress;
-    }
-}

Projects/Server/Network/IConnectionFilter.cs

@@ -0,0 +1,60 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: IConnectionFilter.cs                                            *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Net;
+using System.Threading;
+
+namespace Server.Network;
+
+/// <summary>
+/// A gate consulted for every inbound connection, before the socket is configured and before any
+/// per-connection allocation. Implementations decide membership only — the accept path neither knows
+/// nor cares where a filter's data comes from, so a filter may be a handful of admin-curated entries,
+/// a millions-strong list hydrated from a file, or a query against something else entirely. Core owns
+/// the question; content owns every answer (see <c>Firewall</c> and <c>BlocklistFilter</c> in UOContent).
+/// </summary>
+/// <remarks>
+/// <para>
+/// <see cref="ShouldDeny"/> runs on the game loop once per accepted socket, which is the path that has
+/// to survive a DDoS. Implementations MUST be allocation-free and O(log n) at worst, MUST NOT perform
+/// I/O, and MUST NOT block. Anything expensive (parsing, reloading, reporting to an external service)
+/// belongs off the loop or behind a bounded, non-blocking enqueue.
+/// </para>
+/// <para>
+/// Side effects that a hit implies (contributing to <c>BanChannel</c>, promoting to an OS firewall,
+/// suppressing duplicate reports) are the filter's own business, not the accept path's. This is why
+/// <see cref="ShouldDeny"/> returns a bare bool: the accept path asks one question and does one thing.
+/// </para>
+/// </remarks>
+public interface IConnectionFilter
+{
+    /// <summary>Stable id for logging/config (e.g. <c>firewall</c>, <c>blocklist</c>).</summary>
+    string Name { get; }
+
+    /// <summary>Reads configuration. Called by <see cref="ConnectionFilters.Register"/>. No I/O beyond config.</summary>
+    void Register();
+
+    /// <summary>Starts any background hydration. The token is cancelled on shutdown.</summary>
+    void Start(CancellationToken token);
+
+    /// <summary>Flushes and tears down. Called during shutdown.</summary>
+    void Stop();
+
+    /// <summary>
+    /// True to deny the connection. Must be allocation-free and non-blocking; see the remarks on
+    /// <see cref="IConnectionFilter"/>.
+    /// </summary>
+    bool ShouldDeny(IPAddress address);
+}

Projects/Server/Network/NetState/NetState.Network.cs

@@ -224,10 +224,19 @@ public partial class NetState
                 if (_ipRateLimiter != null && !_ipRateLimiter.Verify(remoteIP, out var totalAttempts))
                 {
                     logger.Debug("{Address} Past IP limit threshold ({TotalAttempts})", remoteIP, totalAttempts);
+
+                    if (Bans.BanConfiguration.Settings.ReportRateLimitTrips)
+                    {
+                        // Enqueue-only contribution; NOT added to the local firewall set (the limiter already
+                        // gates it here and the OS bouncer drops it at the kernel).
+                        Bans.BanChannel.Report(remoteIP, Bans.BanConfiguration.Settings.AutoBanDuration, "rate-limit");
+                    }
                 }
-                else if (Firewall.IsBlocked(remoteIP))
+                else if (ConnectionFilters.ShouldDeny(remoteIP, out var deniedBy))
                 {
-                    logger.Debug("{Address} Firewalled", remoteIP);
+                    // Whatever a hit implies (persisting, promoting to an OS bouncer, contributing to the
+                    // ban channel) is the filter's own business; the accept path just drops the socket.
+                    logger.Debug("{Address} denied by connection filter '{Filter}'", remoteIP, deniedBy);
                 }
                 else
                 {

Projects/Server/Utilities/IPAddressUtility.cs

@@ -0,0 +1,240 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: IPAddressUtility.cs                                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Buffers.Binary;
+using System.Net;
+using System.Net.Sockets;
+using System.Numerics;
+
+namespace Server;
+
+/// <summary>
+/// Low-level IPAddress conversion and parsing helpers shared by the firewall, ban channel, and
+/// blocklist. All members are allocation-free (stack buffers only) so they are safe on hot accept
+/// paths and inside tight parse loops.
+/// </summary>
+public static class IPAddressUtility
+{
+    // Converts an IPAddress to a UInt128 in IPv6 format.
+    // The IsIPv4MappedToIPv6 clause below looks redundant (the BCL only ever sets it on InterNetworkV6),
+    // but it guards the v4 -> UInt128 -> IPAddress round-trip, which can return a mapped v6 address for
+    // what is really a v4 one.
+    //TODO Rework as an explicit "to canonical v6 bits" step that needs no family check
+    //     (see dev-docs/networking-packets.md, "IP Address Normalization")
+    public static UInt128 ToUInt128(this IPAddress ip)
+    {
+        if (ip.AddressFamily == AddressFamily.InterNetwork && !ip.IsIPv4MappedToIPv6)
+        {
+            Span<byte> integer = stackalloc byte[4];
+            return !ip.TryWriteBytes(integer, out _)
+                ? (UInt128)0
+                : new UInt128(0, 0xFFFF00000000UL | BinaryPrimitives.ReadUInt32BigEndian(integer));
+        }
+
+        Span<byte> bytes = stackalloc byte[16];
+        if (!ip.TryWriteBytes(bytes, out _))
+        {
+            return 0;
+        }
+
+        var high = BinaryPrimitives.ReadUInt64BigEndian(bytes[..8]);
+        var low = BinaryPrimitives.ReadUInt64BigEndian(bytes.Slice(8, 8));
+
+        return new UInt128(high, low);
+    }
+
+    // Converts a UInt128 in IPv6 format to an IPAddress
+    public static IPAddress ToIpAddress(this UInt128 value, bool mapToIpv6 = false)
+    {
+        // IPv4 mapped IPv6 address
+        if (!mapToIpv6 && value >= 0xFFFF00000000UL && value <= 0xFFFFFFFFFFFFUL)
+        {
+            var newAddress = IPAddress.HostToNetworkOrder((int)value);
+            return new IPAddress(unchecked((uint)newAddress));
+        }
+
+        Span<byte> bytes = stackalloc byte[16]; // 128 bits for IPv6 address
+        ((IBinaryInteger<UInt128>)value).WriteBigEndian(bytes);
+
+        return new IPAddress(bytes);
+    }
+
+    /// <summary>
+    /// Parses <c>a.b.c.d/n</c>, <c>::/n</c>, or a bare address (treated as a single-host range) into an
+    /// inclusive <see cref="UInt128"/> range in normalized IPv6 form. A bare IPv4 prefix is widened by 96
+    /// bits so v4 and v6 ranges are directly comparable. Returns false on anything malformed.
+    /// </summary>
+    public static bool TryParseCidrRange(ReadOnlySpan<char> cidr, out UInt128 min, out UInt128 max)
+    {
+        min = default;
+        max = default;
+
+        var slash = cidr.IndexOf('/');
+        if (!IPAddress.TryParse(slash >= 0 ? cidr[..slash] : cidr, out var ip))
+        {
+            return false;
+        }
+
+        var isV6 = ip.AddressFamily == AddressFamily.InterNetworkV6;
+        var maxPrefixLength = isV6 ? 128 : 32;
+        int prefixLength;
+
+        if (slash < 0)
+        {
+            prefixLength = maxPrefixLength;
+        }
+        else if (!int.TryParse(cidr[(slash + 1)..], out prefixLength) ||
+                 prefixLength < 0 || prefixLength > maxPrefixLength)
+        {
+            return false;
+        }
+
+        if (!isV6)
+        {
+            prefixLength += 96; // 32 -> 128
+        }
+
+        Span<byte> bytes = stackalloc byte[16];
+        ip.WriteMappedIPv6To(bytes);
+
+        min = Utility.CreateCidrAddress(bytes, prefixLength, false);
+        max = Utility.CreateCidrAddress(bytes, prefixLength, true);
+        return true;
+    }
+
+    /// <summary>Extracts the big-endian uint of an <see cref="AddressFamily.InterNetwork"/> address.</summary>
+    public static bool TryV4(IPAddress ip, out uint v)
+    {
+        Span<byte> b = stackalloc byte[4];
+        if (ip.TryWriteBytes(b, out var n) && n == 4)
+        {
+            v = ((uint)b[0] << 24) | ((uint)b[1] << 16) | ((uint)b[2] << 8) | b[3];
+            return true;
+        }
+
+        v = 0;
+        return false;
+    }
+
+    /// <summary>
+    /// Extracts the embedded v4 uint from a v4-mapped-v6 address directly from the mapped bytes,
+    /// avoiding the allocation of <see cref="IPAddress.MapToIPv4"/>.
+    /// </summary>
+    public static bool TryMappedV4(IPAddress ip, out uint v)
+    {
+        Span<byte> b = stackalloc byte[16];
+        if (ip.TryWriteBytes(b, out var n) && n == 16)
+        {
+            v = ((uint)b[12] << 24) | ((uint)b[13] << 16) | ((uint)b[14] << 8) | b[15];
+            return true;
+        }
+
+        v = 0;
+        return false;
+    }
+
+    /// <summary>Parses a dotted-quad IPv4 literal into a big-endian uint. Allocation-free, strict.</summary>
+    public static bool TryParseV4(ReadOnlySpan<char> s, out uint v)
+    {
+        v = 0;
+        uint acc = 0;
+        int octet = 0, digits = 0, dots = 0;
+        for (var i = 0; i < s.Length; i++)
+        {
+            var c = s[i];
+            if (c == '.')
+            {
+                if (digits == 0 || octet > 255)
+                {
+                    return false;
+                }
+
+                acc = (acc << 8) | (uint)octet;
+                dots++;
+                octet = 0;
+                digits = 0;
+            }
+            else if (c is >= '0' and <= '9')
+            {
+                octet = octet * 10 + (c - '0');
+                if (++digits > 3)
+                {
+                    return false;
+                }
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        if (dots != 3 || digits == 0 || octet > 255)
+        {
+            return false;
+        }
+
+        v = (acc << 8) | (uint)octet;
+        return true;
+    }
+
+    /// <summary>
+    /// UTF-8/ASCII byte overload of <see cref="TryParseV4(ReadOnlySpan{char}, out uint)"/>, mirroring its
+    /// validation exactly so the blocklist can parse dotted-quads straight from file bytes with no
+    /// per-line string allocation.
+    /// </summary>
+    public static bool TryParseV4(ReadOnlySpan<byte> s, out uint v)
+    {
+        v = 0;
+        uint acc = 0;
+        int octet = 0, digits = 0, dots = 0;
+        for (var i = 0; i < s.Length; i++)
+        {
+            var c = s[i];
+            if (c == (byte)'.')
+            {
+                if (digits == 0 || octet > 255)
+                {
+                    return false;
+                }
+
+                acc = (acc << 8) | (uint)octet;
+                dots++;
+                octet = 0;
+                digits = 0;
+            }
+            else if (c is >= (byte)'0' and <= (byte)'9')
+            {
+                octet = octet * 10 + (c - '0');
+                if (++digits > 3)
+                {
+                    return false;
+                }
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        if (dots != 3 || digits == 0 || octet > 255)
+        {
+            return false;
+        }
+
+        v = (acc << 8) | (uint)octet;
+        return true;
+    }
+}

Projects/Server/Utilities/NetworkUtilities.cs

@@ -1,6 +1,7 @@
+using System;
 using System.Net;
 using System.Net.Sockets;
-using Server.Network;
+using Server.Collections;
 
 namespace Server;
 
@@ -14,36 +15,42 @@ public static class NetworkUtilities
             _                            => false
         };
 
-    private static readonly IFirewallEntry[] _privateNetworkV4 =
-    [
-        new CidrFirewallEntry("127.0.0.1/8"),
-        new CidrFirewallEntry("192.168.0.0/16"),
-        new CidrFirewallEntry("10.0.0.0/8"),
-        new CidrFirewallEntry("172.16.0.0/12"),
-        new CidrFirewallEntry("169.254.0.0/16"),
-        new CidrFirewallEntry("100.64.0.0/10")
-    ];
+    // These are constant reserved ranges, not firewall entries -- they only ever answer "is this address
+    // in one of these blocks?", which is exactly what SortedRangeIndex is for. Building them through the
+    // firewall entry types was a convenience that made core depend on the firewall for something that has
+    // nothing to do with banning.
+    private static readonly SortedRangeIndex<UInt128> _privateNetworkV4 = BuildIndex(
+        "127.0.0.1/8",
+        "192.168.0.0/16",
+        "10.0.0.0/8",
+        "172.16.0.0/12",
+        "169.254.0.0/16",
+        "100.64.0.0/10"
+    );
 
-    private static readonly IFirewallEntry[] _privateNetworkV6 =
-    [
-        new CidrFirewallEntry("fc00::/7"),
-        new CidrFirewallEntry("fe80::/10")
-    ];
+    private static readonly SortedRangeIndex<UInt128> _privateNetworkV6 = BuildIndex(
+        "fc00::/7",
+        "fe80::/10"
+    );
 
-    public static bool IsPrivateNetworkV4(this IPAddress ip)
+    private static SortedRangeIndex<UInt128> BuildIndex(params ReadOnlySpan<string> cidrs)
     {
-        for (var i = 0; i < _privateNetworkV4.Length; i++)
+        var ranges = new SortedRangeIndex<UInt128>.Range[cidrs.Length];
+        for (var i = 0; i < cidrs.Length; i++)
         {
-            if (_privateNetworkV4[i].IsBlocked(ip))
+            if (!IPAddressUtility.TryParseCidrRange(cidrs[i], out var min, out var max))
             {
-                return true;
+                throw new ArgumentException($"Invalid reserved-network CIDR \"{cidrs[i]}\"");
             }
+
+            ranges[i] = new SortedRangeIndex<UInt128>.Range(min, max);
         }
 
-        return false;
+        Array.Sort(ranges, SortedRangeIndex<UInt128>.ByMin);
+        return SortedRangeIndex<UInt128>.Build(ranges);
     }
 
-    public static bool IsPrivateNetworkV6(this IPAddress ip) =>
-        _privateNetworkV6[0].IsBlocked(ip) ||
-        _privateNetworkV6[1].IsBlocked(ip);
+    public static bool IsPrivateNetworkV4(this IPAddress ip) => _privateNetworkV4.Contains(ip.ToUInt128());
+
+    public static bool IsPrivateNetworkV6(this IPAddress ip) => _privateNetworkV6.Contains(ip.ToUInt128());
 }

Projects/Server/Utilities/Utility.cs

@@ -108,45 +108,6 @@ public static partial class Utility
         }
     }
 
-    // Converts an IPAddress to a UInt128 in IPv6 format
-    public static UInt128 ToUInt128(this IPAddress ip)
-    {
-        if (ip.AddressFamily == AddressFamily.InterNetwork && !ip.IsIPv4MappedToIPv6)
-        {
-            Span<byte> integer = stackalloc byte[4];
-            return !ip.TryWriteBytes(integer, out _)
-                ? (UInt128)0
-                : new UInt128(0, 0xFFFF00000000UL | BinaryPrimitives.ReadUInt32BigEndian(integer));
-        }
-
-        Span<byte> bytes = stackalloc byte[16];
-        if (!ip.TryWriteBytes(bytes, out _))
-        {
-            return 0;
-        }
-
-        var high = BinaryPrimitives.ReadUInt64BigEndian(bytes[..8]);
-        var low = BinaryPrimitives.ReadUInt64BigEndian(bytes.Slice(8, 8));
-
-        return new UInt128(high, low);
-    }
-
-    // Converts a UInt128 in IPv6 format to an IPAddress
-    public static IPAddress ToIpAddress(this UInt128 value, bool mapToIpv6 = false)
-    {
-        // IPv4 mapped IPv6 address
-        if (!mapToIpv6 && value >= 0xFFFF00000000UL && value <= 0xFFFFFFFFFFFFUL)
-        {
-            var newAddress = IPAddress.HostToNetworkOrder((int)value);
-            return new IPAddress(unchecked((uint)newAddress));
-        }
-
-        Span<byte> bytes = stackalloc byte[16]; // 128 bits for IPv6 address
-        ((IBinaryInteger<UInt128>)value).WriteBigEndian(bytes);
-
-        return new IPAddress(bytes);
-    }
-
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static UInt128 CreateCidrAddress(ReadOnlySpan<byte> bytes, int prefixLength, bool isMax)
     {

Projects/UOContent.Tests/Fixtures/TestServerInitializer.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.IO;
 using System.Reflection;
 using System.Threading;
@@ -61,6 +61,15 @@ internal static class TestServerInitializer
             AssemblyHandler.LoadAssemblies(["Server.dll", "UOContent.dll"]);
 
             SkillsInfo.Configure();
+
+            // Seed the loop clock as Main.cs does before the Configure sweep; otherwise Core.Now is
+            // DateTime.MinValue for the whole test host.
+            Core._now = DateTime.UtcNow;
+
+            // Timer wheel must exist before NetState.Configure(), which schedules a recurring
+            // sweep via Timer.DelayCall (matches production ordering in Main.cs: Timer.Init runs
+            // before AssemblyHandler.Invoke("Configure")).
+            Timer.Init(0);
             Server.Network.NetState.Configure();
             TestMapDefinitions.ConfigureTestMapDefinitions();
 
@@ -91,7 +100,6 @@ internal static class TestServerInitializer
             }
 
             World.Configure();
-            Timer.Init(0);
             RaceDefinitions.Configure();
             MovementImpl.Configure();
             PathFollower.Configure();

Projects/UOContent.Tests/Tests/Network/Bans/Blocklist/BlocklistConfigurationTests.cs

@@ -0,0 +1,65 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistConfigurationTests.cs                                  *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Text.Json;
+using Server.Json;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans.Blocklist;
+
+public class BlocklistConfigurationTests
+{
+    // Locks the JsonConfig casing contract: JsonConfig's options are case-SENSITIVE, so every settings
+    // member must carry an explicit [JsonPropertyName("camelCase")] or it silently binds nothing.
+    [Fact]
+    public void BlocklistSettings_RoundTripsThroughJsonConfig()
+    {
+        var original = new BlocklistSettings
+        {
+            File = "D:/shared/ip-blocklist.txt",
+            ReloadInterval = TimeSpan.FromMinutes(5),
+            ReportHits = false,
+            BanDuration = TimeSpan.FromHours(2),
+            PromoteSuppression = TimeSpan.FromSeconds(30)
+        };
+
+        var json = JsonConfig.Serialize(original);
+
+        Assert.Contains("\"file\"", json);
+        Assert.Contains("\"reloadInterval\"", json);
+        Assert.Contains("\"reportHits\"", json);
+        Assert.Contains("\"banDuration\"", json);
+        Assert.Contains("\"promoteSuppression\"", json);
+
+        var restored = JsonSerializer.Deserialize<BlocklistSettings>(json, JsonConfig.DefaultOptions);
+
+        Assert.NotNull(restored);
+        Assert.Equal(original.File, restored.File);
+        Assert.Equal(original.ReloadInterval, restored.ReloadInterval);
+        Assert.Equal(original.ReportHits, restored.ReportHits);
+        Assert.Equal(original.BanDuration, restored.BanDuration);
+        Assert.Equal(original.PromoteSuppression, restored.PromoteSuppression);
+    }
+
+    // The generator (tools/Export-IpBlocklist.ps1) writes to this path by default; if one side moves
+    // without the other, a shard silently enforces nothing.
+    [Fact]
+    public void Default_file_matches_the_generator_output_path()
+    {
+        Assert.Equal("Configuration/ip-blocklist.txt", new BlocklistSettings().File);
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/Blocklist/BlocklistFileTests.cs

@@ -0,0 +1,85 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistFileTests.cs                                           *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+using System.Net;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans.Blocklist;
+
+public class BlocklistFileTests
+{
+    private static string WriteTemp(string content)
+    {
+        var p = Path.Combine(Path.GetTempPath(), "bl-" + Guid.NewGuid().ToString("N") + ".txt");
+        File.WriteAllText(p, content);
+        return p;
+    }
+
+    [Fact]
+    public void Reads_header_generated_and_count()
+    {
+        var p = WriteTemp("# modernuo-blocklist v1 generated=2026-07-21T09:24:23Z count=2\n1.2.3.4\n5.6.7.0/24\n");
+        Assert.True(BlocklistFile.TryReadHeader(p, out var h));
+        Assert.True(h.Present);
+        Assert.Equal("2026-07-21T09:24:23Z", h.Generated);
+        Assert.Equal(2, h.Count);
+        File.Delete(p);
+    }
+
+    [Fact]
+    public void Missing_file_reports_absent_and_loads_empty()
+    {
+        var p = Path.Combine(Path.GetTempPath(), "does-not-exist-" + Guid.NewGuid().ToString("N"));
+        Assert.False(BlocklistFile.TryReadHeader(p, out var h));
+        Assert.False(h.Present);
+        var snap = BlocklistFile.Load(p, out _, out _);
+        Assert.False(snap.IsBanned(IPAddress.Parse("1.2.3.4")));
+    }
+
+    // Pins the exact line tools/Export-IpBlocklist.ps1 emits: the producer adds informational tokens the
+    // reader doesn't know about, and the reload detector breaks silently if generated= stops being read.
+    [Fact]
+    public void Reads_generator_header_with_extra_tokens()
+    {
+        var p = WriteTemp(
+            "# modernuo-blocklist generated=2026-07-25T18:03:11Z count=12442 ipv4=7868 cidr=4574 feeds=2\n" +
+            "2.181.183.77\n223.169.0.0/16\n"
+        );
+
+        Assert.True(BlocklistFile.TryReadHeader(p, out var h));
+        Assert.Equal("2026-07-25T18:03:11Z", h.Generated);
+        Assert.Equal(12442, h.Count);
+
+        var snap = BlocklistFile.Load(p, out var parsed, out var skipped);
+        Assert.Equal(2, parsed);
+        Assert.Equal(0, skipped);
+        Assert.True(snap.IsBanned(IPAddress.Parse("2.181.183.77")));
+        Assert.True(snap.IsBanned(IPAddress.Parse("223.169.4.9")));
+        File.Delete(p);
+    }
+
+    [Fact]
+    public void Load_parses_body()
+    {
+        var p = WriteTemp("# generated=x count=1\n8.8.8.0/24\n");
+        var snap = BlocklistFile.Load(p, out var parsed, out _);
+        Assert.Equal(1, parsed);
+        Assert.True(snap.IsBanned(IPAddress.Parse("8.8.8.8")));
+        File.Delete(p);
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/Blocklist/BlocklistFilterTests.cs

@@ -0,0 +1,94 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistFilterTests.cs                                         *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Net;
+using System.Text;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans.Blocklist;
+
+// No [Collection] and no static reset hook: the filter is an instance, so each test owns its own
+// snapshot and promote-guard. That is the point of it no longer being a static class.
+public class BlocklistFilterTests
+{
+    private static BlocklistFilter WithList(string list, bool reportHits = true, long suppressionMs = 5000)
+    {
+        var filter = new BlocklistFilter();
+        filter.LoadForTesting(
+            BlocklistSnapshot.Build(Encoding.ASCII.GetBytes(list), out _, out _),
+            reportHits,
+            suppressionMs
+        );
+
+        return filter;
+    }
+
+    [Fact]
+    public void Listed_address_is_denied_and_reported_once_per_window()
+    {
+        var filter = WithList("1.2.3.4");
+        var ip = IPAddress.Parse("1.2.3.4");
+
+        var deny1 = filter.Evaluate(ip, 1000, out var report1);
+        var deny2 = filter.Evaluate(ip, 1500, out var report2);
+        var deny3 = filter.Evaluate(ip, 1000 + 5001, out var report3);
+
+        Assert.True(deny1);
+        Assert.True(report1);
+
+        Assert.True(deny2);
+        Assert.False(report2); // denied again, but promotion suppressed inside the window
+
+        Assert.True(deny3);
+        Assert.True(report3); // window elapsed, promotion may be retried
+    }
+
+    [Fact]
+    public void Unlisted_address_passes()
+    {
+        var filter = WithList("1.2.3.4");
+
+        Assert.False(filter.Evaluate(IPAddress.Parse("9.9.9.9"), 1, out var report));
+        Assert.False(report);
+    }
+
+    [Fact]
+    public void Cidr_membership_is_honored()
+    {
+        var filter = WithList("10.20.30.0/24");
+
+        Assert.True(filter.Evaluate(IPAddress.Parse("10.20.30.255"), 1, out _));
+        Assert.False(filter.Evaluate(IPAddress.Parse("10.20.31.0"), 1, out _));
+    }
+
+    [Fact]
+    public void ReportHits_disabled_still_denies_but_never_promotes()
+    {
+        var filter = WithList("1.2.3.4", reportHits: false);
+
+        Assert.True(filter.Evaluate(IPAddress.Parse("1.2.3.4"), 1, out var report));
+        Assert.False(report);
+    }
+
+    [Fact]
+    public void Unconfigured_filter_denies_nothing()
+    {
+        var filter = new BlocklistFilter();
+
+        Assert.Equal(0, filter.Count);
+        Assert.False(filter.ShouldDeny(IPAddress.Parse("8.8.8.8")));
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/Blocklist/BlocklistSnapshotTests.cs

@@ -0,0 +1,98 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistSnapshotTests.cs                                       *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Net;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans.Blocklist;
+
+public class BlocklistSnapshotTests
+{
+    private static BlocklistSnapshot Build(params string[] lines) =>
+        BlocklistSnapshot.Build(System.Text.Encoding.ASCII.GetBytes(string.Join('\n', lines)), out _, out _);
+
+    [Fact]
+    public void Single_ip_is_matched()
+    {
+        var s = Build("1.2.3.4");
+        Assert.True(s.IsBanned(IPAddress.Parse("1.2.3.4")));
+        Assert.False(s.IsBanned(IPAddress.Parse("1.2.3.5")));
+    }
+
+    [Fact]
+    public void Cidr_contains_and_excludes_boundaries()
+    {
+        var s = Build("10.0.0.0/24");
+        Assert.True(s.IsBanned(IPAddress.Parse("10.0.0.0")));
+        Assert.True(s.IsBanned(IPAddress.Parse("10.0.0.255")));
+        Assert.False(s.IsBanned(IPAddress.Parse("10.0.1.0")));
+        Assert.False(s.IsBanned(IPAddress.Parse("9.255.255.255")));
+    }
+
+    [Fact]
+    public void Comments_blanks_and_garbage_are_skipped_not_thrown()
+    {
+        var s = BlocklistSnapshot.Build(
+            System.Text.Encoding.ASCII.GetBytes(
+                string.Join('\n', "# header generated=x", "", "not-an-ip", "1.2.3.4", "::1", "5.6.7.0/24")),
+            out var parsed, out var skipped);
+        Assert.Equal(3, parsed);      // 1.2.3.4 + ::1 (valid loopback) + 5.6.7.0/24
+        Assert.True(skipped >= 1);    // "not-an-ip"; blank/comment lines are silently skipped, not counted
+        Assert.True(s.IsBanned(IPAddress.Parse("5.6.7.200")));
+    }
+
+    [Fact]
+    public void Empty_snapshot_matches_nothing()
+    {
+        Assert.False(BlocklistSnapshot.Empty.IsBanned(IPAddress.Parse("1.2.3.4")));
+    }
+
+    [Fact]
+    public void Ipv6_single_and_cidr_are_matched()
+    {
+        var s = Build("2001:db8::1", "2001:db8:1::/48");
+        Assert.True(s.IsBanned(IPAddress.Parse("2001:db8::1")));
+        Assert.True(s.IsBanned(IPAddress.Parse("2001:db8:1::abcd")));
+        Assert.False(s.IsBanned(IPAddress.Parse("2001:db8:2::1")));
+    }
+
+    [Fact]
+    public void Ipv4_mapped_ipv6_is_normalized_to_v4()
+    {
+        var s = Build("1.2.3.4");
+        Assert.True(s.IsBanned(IPAddress.Parse("::ffff:1.2.3.4"))); // must not bypass the v4 set
+    }
+
+    [Fact]
+    public void Nested_cidr_intervals_are_coalesced()
+    {
+        // A /32 nested inside a /24: InRange's binary search only inspects the
+        // rightmost interval starting <= ip, so without coalescing an IP inside
+        // the /24 but outside the /32 would land on the /32 and wrongly pass.
+        var s = Build("10.0.0.0/24", "10.0.0.5/32");
+        Assert.True(s.IsBanned(IPAddress.Parse("10.0.0.100"))); // inside /24, outside /32
+        Assert.True(s.IsBanned(IPAddress.Parse("10.0.0.5")));   // the nested /32 itself
+        Assert.False(s.IsBanned(IPAddress.Parse("10.0.1.0")));  // genuinely outside both
+    }
+
+    [Fact]
+    public void Overlapping_cidr_intervals_are_coalesced()
+    {
+        var s = Build("10.0.0.0/25", "10.0.0.64/25");
+        Assert.True(s.IsBanned(IPAddress.Parse("10.0.0.100")));  // covered by the second /25
+        Assert.False(s.IsBanned(IPAddress.Parse("10.0.0.200"))); // outside both
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/Blocklist/PromotedGuardTests.cs

@@ -0,0 +1,46 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: PromotedGuardTests.cs                                           *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using Server.Network.Bans;
+using Xunit;
+
+namespace Server.Tests.Network.Bans.Blocklist;
+
+public class PromotedGuardTests
+{
+    [Fact]
+    public void First_mark_true_then_suppressed_until_ttl()
+    {
+        var g = new PromotedGuard();
+        Assert.True(g.TryMark((UInt128)42, 1000, 5000));
+        Assert.False(g.TryMark((UInt128)42, 2000, 5000)); // within TTL
+        Assert.True(g.TryMark((UInt128)42, 6001, 5000));  // expired → re-mark
+    }
+
+    [Fact]
+    public void Sweep_removes_expired_entries_allowing_remark()
+    {
+        var g = new PromotedGuard();
+        Assert.True(g.TryMark((UInt128)7, 0, 1000));
+        Assert.False(g.TryMark((UInt128)7, 500, 1000)); // still within TTL
+
+        g.Sweep(500); // not yet expired, sweep should not remove it
+        Assert.False(g.TryMark((UInt128)7, 999, 1000));
+
+        g.Sweep(1001); // now expired, sweep removes it
+        Assert.True(g.TryMark((UInt128)7, 1002, 1000)); // fresh mark, not "still marked"
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/CrowdSecAlertClientTests.cs

@@ -0,0 +1,51 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecAlertClientTests.cs                                     *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Net;
+using Server.Network.Bans.CrowdSec;
+using Xunit;
+
+namespace Server.Tests.Network.Bans;
+
+public class CrowdSecAlertClientTests
+{
+    [Fact]
+    public void BuildDeleteQuery_EscapesOrigin()
+    {
+        // origin is operator-controlled config (crowdsec.json), so it must be treated as untrusted
+        // input going into the URL, same as any other interpolated value.
+        var query = CrowdSecAlertClient.BuildDeleteQuery("modern uo/test&x=1", IPAddress.Parse("1.2.3.4"));
+
+        Assert.Equal("/v1/decisions?origin=modern%20uo%2Ftest%26x%3D1&ip=1.2.3.4", query);
+    }
+
+    [Fact]
+    public void BuildDeleteQuery_PlainOrigin_Ipv4()
+    {
+        var query = CrowdSecAlertClient.BuildDeleteQuery("modernuo", IPAddress.Parse("192.168.1.1"));
+
+        Assert.Equal("/v1/decisions?origin=modernuo&ip=192.168.1.1", query);
+    }
+
+    [Fact]
+    public void BuildDeleteQuery_Ipv6_IsEscaped()
+    {
+        // IPv6 textual form contains ':', which Uri.EscapeDataString percent-encodes like any other
+        // reserved character — confirms the escaping is applied uniformly, not just for IPv4.
+        var query = CrowdSecAlertClient.BuildDeleteQuery("modernuo", IPAddress.Parse("2001:db8::1"));
+
+        Assert.Equal("/v1/decisions?origin=modernuo&ip=2001%3Adb8%3A%3A1", query);
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/CrowdSecConfigurationTests.cs

@@ -0,0 +1,82 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecConfigurationTests.cs                                   *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Text.Json;
+using Server.Json;
+using Server.Network.Bans.CrowdSec;
+using Xunit;
+
+namespace Server.Tests.Network.Bans;
+
+public class CrowdSecConfigurationTests
+{
+    // Locks the JsonConfig casing/converter contract: JsonConfig's options are case-SENSITIVE, so
+    // every settings member must carry an explicit [JsonPropertyName("camelCase")] or it silently
+    // binds nothing. These tests round-trip through the exact options the loader uses.
+
+    [Fact]
+    public void CrowdSecSettings_RoundTripsThroughJsonConfig()
+    {
+        var original = new CrowdSecSettings
+        {
+            LapiUrl = "http://10.0.0.5:9090",
+            MachineId = "shard",
+            Password = "secret",
+            Origin = "modernuo",
+            ManualBanDuration = TimeSpan.FromHours(168),
+            FlushInterval = TimeSpan.FromSeconds(1),
+            MaxQueue = 10000
+        };
+
+        var json = JsonConfig.Serialize(original);
+
+        // camelCase property names must be present (not PascalCase) or the case-sensitive reader binds nothing.
+        Assert.Contains("\"lapiUrl\"", json);
+        Assert.Contains("\"machineId\"", json);
+        Assert.Contains("\"password\"", json);
+        Assert.Contains("\"origin\"", json);
+        Assert.Contains("\"manualBanDuration\"", json);
+        Assert.Contains("\"flushInterval\"", json);
+        Assert.Contains("\"maxQueue\"", json);
+
+        var restored = JsonSerializer.Deserialize<CrowdSecSettings>(json, JsonConfig.DefaultOptions);
+
+        Assert.NotNull(restored);
+        Assert.Equal(original.LapiUrl, restored.LapiUrl);
+        Assert.Equal(original.MachineId, restored.MachineId);
+        Assert.Equal(original.Password, restored.Password);
+        Assert.Equal(original.Origin, restored.Origin);
+        Assert.Equal(original.ManualBanDuration, restored.ManualBanDuration); // TimeSpan survives
+        Assert.Equal(original.FlushInterval, restored.FlushInterval);        // TimeSpan survives
+        Assert.Equal(original.MaxQueue, restored.MaxQueue);
+        Assert.True(restored.ReportingEnabled);
+    }
+
+    [Fact]
+    public void CrowdSecSettings_Defaults_AreReportingDisabledLocalLoopback()
+    {
+        var settings = new CrowdSecSettings();
+
+        Assert.Equal("http://127.0.0.1:8080", settings.LapiUrl);
+        Assert.Equal("", settings.MachineId);
+        Assert.Equal("", settings.Password);
+        Assert.Equal("modernuo", settings.Origin);
+        Assert.Equal(TimeSpan.FromHours(168), settings.ManualBanDuration);
+        Assert.Equal(TimeSpan.FromSeconds(1), settings.FlushInterval);
+        Assert.Equal(10000, settings.MaxQueue);
+        Assert.False(settings.ReportingEnabled); // empty machineId/password => inert
+    }
+}

Projects/UOContent.Tests/Tests/Network/Bans/CrowdSecReporterTests.cs

@@ -0,0 +1,229 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecReporterTests.cs                                        *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using Server.Network.Bans.CrowdSec;
+using Xunit;
+
+namespace Server.Tests.Network.Bans;
+
+public class CrowdSecReporterTests
+{
+    private static CrowdSecSettings Settings() => new()
+    {
+        MachineId = "shard",
+        Password = "secret",
+        Origin = "modernuo",
+        ManualBanDuration = TimeSpan.FromHours(168)
+    };
+
+    [Fact]
+    public void BuildAlerts_DedupsByIp()
+    {
+        var now = DateTime.UnixEpoch;
+        var items = new List<CrowdSecReporter.ReportItem>
+        {
+            new(IPAddress.Parse("1.1.1.1"), TimeSpan.FromHours(1), "rate-limit", false),
+            new(IPAddress.Parse("1.1.1.1"), TimeSpan.FromHours(1), "rate-limit", false),
+            new(IPAddress.Parse("2.2.2.2"), TimeSpan.FromHours(1), "rate-limit", false)
+        };
+
+        var alerts = CrowdSecReporter.BuildAlerts(items, Settings(), now);
+
+        Assert.Equal(2, alerts.Count);
+        Assert.All(alerts, a => Assert.Single(a.Decisions));
+        Assert.Contains(alerts, a => a.Source.Value == "1.1.1.1");
+        Assert.Contains(alerts, a => a.Source.Value == "2.2.2.2");
+    }
+
+    [Fact]
+    public void BuildAlerts_ScenarioFromReason_OriginFromSettings()
+    {
+        var alerts = CrowdSecReporter.BuildAlerts(
+            [new(IPAddress.Parse("3.3.3.3"), TimeSpan.FromHours(1), "manual", false)],
+            Settings(),
+            DateTime.UnixEpoch);
+
+        var decision = Assert.Single(alerts).Decisions[0];
+        Assert.Equal("modernuo/manual", alerts[0].Scenario);
+        Assert.Equal("modernuo", decision.Origin);
+        Assert.Equal("ban", decision.Type);
+        Assert.Equal("Ip", decision.Scope);
+        Assert.Equal("3.3.3.3", decision.Value);
+    }
+
+    [Fact]
+    public void BuildAlerts_ScenarioFromReason_Blocklist()
+    {
+        var alerts = CrowdSecReporter.BuildAlerts(
+            [new(IPAddress.Parse("5.5.5.5"), TimeSpan.FromHours(1), "blocklist", false)],
+            Settings(),
+            DateTime.UnixEpoch);
+
+        var decision = Assert.Single(alerts).Decisions[0];
+        Assert.Equal("modernuo/blocklist", alerts[0].Scenario);
+        Assert.Equal("modernuo/blocklist", decision.Scenario);
+    }
+
+    [Fact]
+    public void FormatDuration_UsesSeconds_FloorsAtOne()
+    {
+        Assert.Equal("3600s", CrowdSecReporter.FormatDuration(TimeSpan.FromHours(1)));
+        Assert.Equal("1s", CrowdSecReporter.FormatDuration(TimeSpan.Zero));
+        Assert.Equal("1s", CrowdSecReporter.FormatDuration(TimeSpan.FromMilliseconds(10)));
+    }
+
+    [Fact]
+    public void Report_WhenQueueFull_DropsAndCounts()
+    {
+        var reporter = new CrowdSecReporter(new NullAlertClient(), new CrowdSecSettings
+        {
+            MachineId = "shard",
+            Password = "secret",
+            MaxQueue = 2
+        });
+        // Do NOT Start() the drain — so the queue fills and overflows deterministically.
+
+        for (var i = 0; i < 10; i++)
+        {
+            reporter.Report(IPAddress.Parse("4.4.4." + i), TimeSpan.FromHours(1), "rate-limit");
+        }
+
+        Assert.True(reporter.DroppedCount >= 8);
+    }
+
+    // Stop() without a prior Start() drives FlushRemainingOnStop() synchronously (no drain task, no
+    // Task.Delay backoff involved), so this is deterministic — no wall-clock timing dependency.
+    [Fact]
+    public void Stop_FlushesQueuedReports_ViaClient()
+    {
+        var client = new RecordingAlertClient();
+        var reporter = new CrowdSecReporter(client, Settings());
+
+        reporter.Report(IPAddress.Parse("6.6.6.6"), TimeSpan.FromHours(1), "rate-limit");
+        reporter.Stop();
+
+        var posted = Assert.Single(client.Posted);
+        Assert.Equal("6.6.6.6", Assert.Single(posted).Source.Value);
+        Assert.Equal(0, reporter.SendFailureCount);
+    }
+
+    [Fact]
+    public void Stop_FlushesQueuedRetracts_ViaClient()
+    {
+        var client = new RecordingAlertClient();
+        var reporter = new CrowdSecReporter(client, Settings());
+
+        reporter.Retract(IPAddress.Parse("8.8.8.8"));
+        reporter.Stop();
+
+        Assert.Equal(IPAddress.Parse("8.8.8.8"), Assert.Single(client.Deleted));
+        Assert.Equal(0, reporter.SendFailureCount);
+    }
+
+    [Fact]
+    public void Stop_WhenFlushSendFails_CountsSendFailure()
+    {
+        var reporter = new CrowdSecReporter(new ThrowingAlertClient(), Settings());
+
+        reporter.Report(IPAddress.Parse("7.7.7.7"), TimeSpan.FromHours(1), "rate-limit");
+        reporter.Stop();
+
+        Assert.Equal(1, reporter.SendFailureCount);
+    }
+
+    [Fact]
+    public void Stop_WithEmptyQueue_DoesNotInvokeClientOrFail()
+    {
+        var client = new RecordingAlertClient();
+        var reporter = new CrowdSecReporter(client, Settings());
+
+        reporter.Stop();
+
+        Assert.Empty(client.Posted);
+        Assert.Equal(0, reporter.SendFailureCount);
+    }
+
+    /// <summary>
+    /// The drain task must track the loop's lifetime, not just its first await — a ValueTask-returning
+    /// drain loop passed to Task.Run yields a Task&lt;ValueTask&gt; that completes immediately, which makes
+    /// Stop()'s drain-exited handshake a no-op. With an empty queue the loop parks on WaitToReadAsync,
+    /// so a correctly unwrapped task cannot win this race; a slow pool only under-detects.
+    /// </summary>
+    [Fact]
+    public async Task Start_DrainTaskSpansLoopLifetime_NotJustTheFirstAwait()
+    {
+        var reporter = new CrowdSecReporter(new NullAlertClient(), Settings());
+        using var cts = new CancellationTokenSource();
+
+        reporter.Start(cts.Token);
+
+        var drain = reporter.DrainTaskForTesting;
+        Assert.NotNull(drain);
+
+        var first = await Task.WhenAny(drain, Task.Delay(TimeSpan.FromMilliseconds(500)));
+        Assert.False(ReferenceEquals(first, drain), "drain task completed while the loop was still running");
+
+        reporter.Stop();
+
+        Assert.True(drain.IsCompleted, "Stop() returned before the drain loop exited");
+    }
+
+    private sealed class NullAlertClient : ICrowdSecAlertClient
+    {
+        public ValueTask PostAlertsAsync(IReadOnlyList<CrowdSecAlert> alerts, CancellationToken token) =>
+            ValueTask.CompletedTask;
+
+        public ValueTask DeleteDecisionsAsync(string origin, IPAddress ip, CancellationToken token) =>
+            ValueTask.CompletedTask;
+
+        public void Dispose() { }
+    }
+
+    private sealed class RecordingAlertClient : ICrowdSecAlertClient
+    {
+        public List<IReadOnlyList<CrowdSecAlert>> Posted { get; } = [];
+        public List<IPAddress> Deleted { get; } = [];
+
+        public ValueTask PostAlertsAsync(IReadOnlyList<CrowdSecAlert> alerts, CancellationToken token)
+        {
+            Posted.Add(alerts);
+            return ValueTask.CompletedTask;
+        }
+
+        public ValueTask DeleteDecisionsAsync(string origin, IPAddress ip, CancellationToken token)
+        {
+            Deleted.Add(ip);
+            return ValueTask.CompletedTask;
+        }
+
+        public void Dispose() { }
+    }
+
+    private sealed class ThrowingAlertClient : ICrowdSecAlertClient
+    {
+        public ValueTask PostAlertsAsync(IReadOnlyList<CrowdSecAlert> alerts, CancellationToken token) =>
+            throw new InvalidOperationException("simulated LAPI outage");
+
+        public ValueTask DeleteDecisionsAsync(string origin, IPAddress ip, CancellationToken token) =>
+            ValueTask.CompletedTask;
+
+        public void Dispose() { }
+    }
+}

Projects/UOContent.Tests/Tests/Network/Firewall/FirewallPersistenceTests.cs

@@ -0,0 +1,72 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: FirewallPersistenceTests.cs                                     *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Net;
+using Server.Network;
+using Xunit;
+
+namespace Server.Tests.Network.Firewall;
+
+[Collection("Sequential UOContent Tests")]
+public class FirewallPersistenceTests
+{
+    [Fact]
+    public void ToSettings_RoundTrips_PermanentAndTtl()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        Server.Network.Firewall.Add(new SingleIpFirewallEntry(IPAddress.Parse("1.2.3.4")));
+        Server.Network.Firewall.Add(new SingleIpFirewallEntry(IPAddress.Parse("2.2.2.2")), TimeSpan.FromHours(1));
+
+        var settings = Server.Network.Firewall.ToSettings();
+
+        Server.Network.Firewall.ResetForTesting();
+        Server.Network.Firewall.LoadFrom(settings);
+
+        Assert.True(Server.Network.Firewall.IsBlocked(IPAddress.Parse("1.2.3.4")));
+        Assert.True(Server.Network.Firewall.IsBlocked(IPAddress.Parse("2.2.2.2")));
+    }
+
+    [Fact]
+    public void LoadFrom_SkipsAlreadyExpired()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        var settings = new FirewallSettings
+        {
+            Entries =
+            [
+                // Core.Now, matching the clock LoadFrom compares against.
+                new FirewallEntryRecord { Value = "9.9.9.9", Expires = Core.Now.AddHours(-1) }
+            ]
+        };
+
+        Server.Network.Firewall.LoadFrom(settings);
+
+        Assert.False(Server.Network.Firewall.IsBlocked(IPAddress.Parse("9.9.9.9")));
+    }
+
+    [Fact]
+    public void ToSettings_OmitsExpiryForPermanent()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        Server.Network.Firewall.Add(new SingleIpFirewallEntry(IPAddress.Parse("1.2.3.4")));
+
+        var settings = Server.Network.Firewall.ToSettings();
+
+        Assert.Single(settings.Entries);
+        Assert.Null(settings.Entries[0].Expires);
+        Assert.Equal("1.2.3.4", settings.Entries[0].Value);
+    }
+}

Projects/UOContent.Tests/Tests/Network/Firewall/FirewallTests.cs

@@ -0,0 +1,89 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: FirewallTests.cs                                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Net;
+using Server.Network;
+using Xunit;
+
+namespace Server.Tests.Network.Firewall;
+
+[Collection("Sequential UOContent Tests")]
+public class FirewallTests
+{
+    private static IPAddress Ip(string s) => IPAddress.Parse(s);
+
+    [Fact]
+    public void Add_ThenIsBlocked_SingleIp()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        Assert.True(Server.Network.Firewall.Add(new SingleIpFirewallEntry(Ip("1.2.3.4"))));
+        Assert.True(Server.Network.Firewall.IsBlocked(Ip("1.2.3.4")));
+        Assert.False(Server.Network.Firewall.IsBlocked(Ip("1.2.3.5")));
+    }
+
+    [Fact]
+    public void Add_Range_BlocksInside_NotOutside()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        Server.Network.Firewall.Add(new CidrFirewallEntry(Ip("10.0.0.0"), Ip("10.0.0.255")));
+        Assert.True(Server.Network.Firewall.IsBlocked(Ip("10.0.0.7")));
+        Assert.False(Server.Network.Firewall.IsBlocked(Ip("10.0.1.0")));
+    }
+
+    [Fact]
+    public void Remove_Unblocks()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        var entry = new SingleIpFirewallEntry(Ip("1.2.3.4"));
+        Server.Network.Firewall.Add(entry);
+        Assert.True(Server.Network.Firewall.Remove(entry));
+        Assert.False(Server.Network.Firewall.IsBlocked(Ip("1.2.3.4")));
+    }
+
+    [Fact]
+    public void ExpireEntries_RemovesExpired_KeepsPermanent()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        var permanent = new SingleIpFirewallEntry(Ip("1.1.1.1"));
+        var temporary = new SingleIpFirewallEntry(Ip("2.2.2.2"));
+        Server.Network.Firewall.Add(permanent);                                   // no ttl
+        Server.Network.Firewall.Add(temporary, TimeSpan.FromMilliseconds(50));    // ttl
+
+        Server.Network.Firewall.ExpireEntries(Core.TickCount + 100);              // past the ttl
+
+        Assert.True(Server.Network.Firewall.IsBlocked(Ip("1.1.1.1")));
+        Assert.False(Server.Network.Firewall.IsBlocked(Ip("2.2.2.2")));
+    }
+
+    [Fact]
+    public void ToFirewallEntry_ParsesForms()
+    {
+        Assert.IsType<SingleIpFirewallEntry>(Server.Network.Firewall.ToFirewallEntry("1.2.3.4"));
+        Assert.IsType<CidrFirewallEntry>(Server.Network.Firewall.ToFirewallEntry("10.0.0.0/24"));
+        Assert.IsType<CidrFirewallEntry>(Server.Network.Firewall.ToFirewallEntry("10.0.0.0-10.0.0.255"));
+        Assert.Null(Server.Network.Firewall.ToFirewallEntry("not-an-ip"));
+    }
+
+    [Fact]
+    public void ReadFirewallSet_SurfacesAddedEntries()
+    {
+        Server.Network.Firewall.ResetForTesting();
+        var entry = new SingleIpFirewallEntry(Ip("1.2.3.4"));
+        Server.Network.Firewall.Add(entry);
+
+        Server.Network.Firewall.ReadFirewallSet(set => Assert.Contains(entry, set));
+    }
+}

Projects/UOContent/Commands/Generic/Commands/Commands.cs

@@ -9,6 +9,7 @@ using Server.Items;
 using Server.Mobiles;
 using Server.Multis;
 using Server.Network;
+using Server.Network.Bans;
 using Server.Spells;
 
 namespace Server.Commands.Generic
@@ -1154,7 +1155,8 @@ namespace Server.Commands.Generic
 
                 try
                 {
-                    AdminFirewall.Add(state.Address);
+                    Firewall.Add(new SingleIpFirewallEntry(state.Address));
+                    BanChannel.Report(state.Address, TimeSpan.Zero, "manual");
                     AddResponse("They have been firewalled.");
                 }
                 catch (Exception ex)

Projects/UOContent/Gumps/AdminGump.cs

@@ -11,6 +11,7 @@ using Server.Maps;
 using Server.Misc;
 using Server.Multis;
 using Server.Network;
+using Server.Network.Bans;
 using Server.Prompts;
 using Server.Saves;
 using Server.Text;
@@ -1743,7 +1744,8 @@ namespace Server.Gumps
             {
                 for (var i = 0; i < a.LoginIPs.Length; ++i)
                 {
-                    AdminFirewall.Add(a.LoginIPs[i]);
+                    Firewall.Add(new SingleIpFirewallEntry(a.LoginIPs[i]));
+                    BanChannel.Report(a.LoginIPs[i], TimeSpan.Zero, "manual");
                 }
 
                 notice = "All addresses in the list have been firewalled.";
@@ -1767,7 +1769,13 @@ namespace Server.Gumps
 
             if (okay)
             {
-                AdminFirewall.Add(toFirewall);
+                var firewallEntry = Firewall.ToFirewallEntry(toFirewall);
+                Firewall.Add(firewallEntry);
+
+                if (firewallEntry.MinIpAddress == firewallEntry.MaxIpAddress)
+                {
+                    BanChannel.Report(firewallEntry.MinIpAddress.ToIpAddress(), TimeSpan.Zero, "manual");
+                }
 
                 notice = $"{toFirewall} : Added to firewall.";
             }
@@ -3559,7 +3567,7 @@ namespace Server.Gumps
                                         IFirewallEntry firewallEntry;
                                         try
                                         {
-                                            firewallEntry = AdminFirewall.ToFirewallEntry(text);
+                                            firewallEntry = Firewall.ToFirewallEntry(text);
                                         }
                                         catch
                                         {
@@ -3581,7 +3589,17 @@ namespace Server.Gumps
                                             $"{from.AccessLevel} {CommandLogging.Format(from)} firewalling {firewallEntry}"
                                         );
 
-                                        AdminFirewall.Add(firewallEntry);
+                                        Firewall.Add(firewallEntry);
+
+                                        if (firewallEntry.MinIpAddress == firewallEntry.MaxIpAddress)
+                                        {
+                                            BanChannel.Report(
+                                                firewallEntry.MinIpAddress.ToIpAddress(),
+                                                TimeSpan.Zero,
+                                                "manual"
+                                            );
+                                        }
+
                                         from.SendGump(
                                             new AdminGump(
                                                 from,
@@ -3620,7 +3638,13 @@ namespace Server.Gumps
                                             $"{from.AccessLevel} {CommandLogging.Format(from)} removing {m_State} from firewall list"
                                         );
 
-                                        AdminFirewall.Remove(m_State);
+                                        Firewall.Remove(m_State as IFirewallEntry);
+
+                                        if (m_State is IFirewallEntry fe && fe.MinIpAddress == fe.MaxIpAddress)
+                                        {
+                                            BanChannel.Retract(fe.MinIpAddress.ToIpAddress());
+                                        }
+
                                         from.SendGump(
                                             new AdminGump(
                                                 from,

Projects/UOContent/Misc/AdminFirewall.cs

@@ -1,139 +0,0 @@
-using System;
-using System.Buffers;
-using System.IO;
-using System.Net;
-using System.Runtime.CompilerServices;
-using Server.Logging;
-using Server.Network;
-
-namespace Server;
-
-public static class AdminFirewall
-{
-    private static readonly ILogger logger = LogFactory.GetLogger(typeof(AdminFirewall));
-
-    private const string firewallConfigPath = "firewall.cfg";
-
-    public static void Configure()
-    {
-        if (File.Exists(firewallConfigPath))
-        {
-            var searchValues = SearchValues.Create("*Xx?");
-
-            using var ip = new StreamReader(firewallConfigPath);
-
-            while (ip.ReadLine() is { } line)
-            {
-                line = line.Trim();
-
-                if (line.Length == 0)
-                {
-                    continue;
-                }
-
-                if (line.AsSpan().ContainsAny(searchValues))
-                {
-                    logger.Warning("Legacy firewall entry \"{Entry}\" ignored", line);
-                    continue;
-                }
-
-                Add(ToFirewallEntry(line), false);
-            }
-        }
-    }
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static IFirewallEntry ToFirewallEntry(object entry)
-    {
-        return entry switch
-        {
-            IFirewallEntry firewallEntry => firewallEntry,
-            IPAddress address            => new SingleIpFirewallEntry(address),
-            string s                     => ToFirewallEntry(s),
-            _                            => null
-        };
-    }
-
-    public static IFirewallEntry ToFirewallEntry(string entry)
-    {
-        if (entry == null)
-        {
-            return null;
-        }
-
-        try
-        {
-            var rangeSeparator = entry.IndexOf('-');
-            if (rangeSeparator > -1)
-            {
-                return new CidrFirewallEntry(
-                    IPAddress.Parse(entry.AsSpan(0, rangeSeparator)),
-                    IPAddress.Parse(entry.AsSpan(rangeSeparator + 1))
-                );
-            }
-
-            // CIDR notation
-            if (entry.IndexOf('/') > -1)
-            {
-                return new CidrFirewallEntry(entry);
-            }
-
-            return new SingleIpFirewallEntry(entry);
-        }
-        catch
-        {
-            return null;
-        }
-    }
-
-    public static bool Remove(object obj, bool save = true)
-    {
-        var entry = ToFirewallEntry(obj);
-
-        if (entry == null)
-        {
-            return false;
-        }
-
-        if (!Firewall.Remove(entry))
-        {
-            return false;
-        }
-
-        if (save)
-        {
-            Save();
-        }
-
-        return true;
-    }
-
-    public static void Add(object obj) => Add(ToFirewallEntry(obj));
-
-    public static bool Add(IFirewallEntry entry, bool save = true)
-    {
-        if (!Firewall.Add(entry))
-        {
-            return false;
-        }
-
-        if (save)
-        {
-            Save();
-        }
-
-        return true;
-    }
-
-    public static void Save()
-    {
-        Firewall.ReadFirewallSet(firewallSet =>
-        {
-            using var op = new StreamWriter(firewallConfigPath);
-            foreach (var entry in firewallSet)
-            {
-                op.WriteLine(entry);
-            }
-        });
-    }
-}

Projects/UOContent/Misc/Blocklist/BlocklistConfiguration.cs

@@ -0,0 +1,90 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistConfiguration.cs                                       *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+using System.Text.Json.Serialization;
+using Server.Json;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// Loads the <see cref="BlocklistSettings"/> from <c>Configuration/blocklist.json</c> (matching the
+/// per-feature JSON config pattern used by <c>AssistantConfiguration</c>). Loaded once; a missing file
+/// writes a template so operators have something to edit.
+/// </summary>
+public static class BlocklistConfiguration
+{
+    private const string _path = "Configuration/blocklist.json";
+
+    public static BlocklistSettings Settings { get; private set; }
+
+    public static void Load()
+    {
+        var path = Path.Join(Core.BaseDirectory, _path);
+
+        if (File.Exists(path))
+        {
+            Settings = JsonConfig.Deserialize<BlocklistSettings>(path);
+        }
+        else
+        {
+            Settings = new BlocklistSettings();
+            Save();
+        }
+    }
+
+    private static void Save()
+    {
+        JsonConfig.Serialize(Path.Join(Core.BaseDirectory, _path), Settings);
+    }
+}
+
+/// <summary>
+/// Bound configuration for <see cref="BlocklistFilter"/>. The filter is inert unless <see cref="File"/>
+/// points at a list that actually exists, so the shipped defaults are safe on a shard that never runs
+/// the generator.
+/// </summary>
+public record BlocklistSettings
+{
+    /// <summary>
+    /// Path to the blocklist. A relative path resolves against <see cref="Core.BaseDirectory"/>; an
+    /// absolute path is used as-is (handy when several shards share one generated list). Set to
+    /// <c>""</c> to disable the gate entirely. Produce the file with <c>tools/Export-IpBlocklist.ps1</c>.
+    /// </summary>
+    [JsonPropertyName("file")]
+    public string File { get; set; } = "Configuration/ip-blocklist.txt";
+
+    /// <summary>How often the file is checked for changes. Reloads only happen when it actually changed.</summary>
+    [JsonPropertyName("reloadInterval")]
+    public TimeSpan ReloadInterval { get; set; } = TimeSpan.FromSeconds(60);
+
+    /// <summary>Whether blocklist hits are contributed to the ban channel (the demand-paging promotion).</summary>
+    [JsonPropertyName("reportHits")]
+    public bool ReportHits { get; set; } = true;
+
+    /// <summary>Duration reported for a blocklist-matched ban.</summary>
+    [JsonPropertyName("banDuration")]
+    public TimeSpan BanDuration { get; set; } = TimeSpan.FromHours(6);
+
+    /// <summary>
+    /// How long the accept-path guard suppresses re-reporting a promoted address. This only needs to
+    /// bridge the gap until the OS bouncer picks up the promotion (seconds); after that the kernel drops
+    /// repeat traffic. Decoupled from <see cref="BanDuration"/> so the guard doesn't have to remember
+    /// hours' worth of distinct addresses.
+    /// </summary>
+    [JsonPropertyName("promoteSuppression")]
+    public TimeSpan PromoteSuppression { get; set; } = TimeSpan.FromSeconds(60);
+}

Projects/UOContent/Misc/Blocklist/BlocklistFile.cs

@@ -0,0 +1,86 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistFile.cs                                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+
+namespace Server.Network.Bans;
+
+public readonly record struct BlocklistHeader(string Generated, int Count, bool Present);
+
+/// <summary>Reads the versioned blocklist file: cheap header probe + full snapshot load.</summary>
+public static class BlocklistFile
+{
+    public static bool TryReadHeader(string path, out BlocklistHeader header)
+    {
+        header = new BlocklistHeader(null, 0, false);
+        try
+        {
+            if (!File.Exists(path))
+            {
+                return false;
+            }
+            using var reader = new StreamReader(path);
+            var first = reader.ReadLine();
+            if (first == null)
+            {
+                header = new BlocklistHeader(null, 0, true);
+                return true;
+            }
+            string generated = null;
+            var count = 0;
+            if (first.StartsWith('#'))
+            {
+                var tokens = first.Split(' ', StringSplitOptions.RemoveEmptyEntries);
+                for (var i = 0; i < tokens.Length; i++)
+                {
+                    var tok = tokens[i];
+                    if (tok.StartsWith("generated=", StringComparison.Ordinal))
+                    {
+                        generated = tok["generated=".Length..];
+                    }
+                    else if (tok.StartsWith("count=", StringComparison.Ordinal))
+                    {
+                        int.TryParse(tok["count=".Length..], out count);
+                    }
+                }
+            }
+            header = new BlocklistHeader(generated, count, true);
+            return true;
+        }
+        catch
+        {
+            return false; // treat as absent; caller keeps last-good / empty
+        }
+    }
+
+    public static BlocklistSnapshot Load(string path, out int parsed, out int skipped)
+    {
+        parsed = 0;
+        skipped = 0;
+        try
+        {
+            if (!File.Exists(path))
+            {
+                return BlocklistSnapshot.Empty;
+            }
+            return BlocklistSnapshot.Build(File.ReadAllBytes(path), out parsed, out skipped);
+        }
+        catch
+        {
+            return BlocklistSnapshot.Empty;
+        }
+    }
+}

Projects/UOContent/Misc/Blocklist/BlocklistFilter.cs

@@ -0,0 +1,259 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistFilter.cs                                              *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+using System.Net;
+using System.Threading;
+using System.Threading.Tasks;
+using Server.Logging;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// Accept-path gate for a large, file-sourced IP blocklist, hydrated from the file a generator
+/// (<c>tools/Export-IpBlocklist.ps1</c>) writes on a schedule. Holds an immutable snapshot swapped
+/// atomically by an off-loop reload poll, so accept-path reads are lock-free. Inert when no file is
+/// configured or present.
+/// </summary>
+/// <remarks>
+/// This is the demand-paging half of the design: an OS firewall cannot hold millions of entries on
+/// Windows, so the millions live here and only addresses that actually connect are promoted to CrowdSec
+/// (and from there to the OS firewall) through <see cref="BanChannel"/>. <see cref="PromotedGuard"/>
+/// keeps a flood of repeat connections from re-reporting the same address before the bouncer picks it up.
+/// </remarks>
+public sealed class BlocklistFilter : IConnectionFilter
+{
+    private static readonly ILogger logger = LogFactory.GetLogger(typeof(BlocklistFilter));
+
+    // Written by the reload poll (off-loop), read by the accept path (game loop): a single volatile
+    // reference swap is the whole synchronization story — readers see the old or the new snapshot, whole.
+    private volatile BlocklistSnapshot _snapshot = BlocklistSnapshot.Empty;
+
+    private readonly PromotedGuard _guard = new();
+
+    private string _path;
+    private TimeSpan _interval;
+    private bool _reportHits;
+    private TimeSpan _banDuration;
+    private long _suppressionMs;
+    private string _lastGenerated;
+    private DateTime _lastWriteUtc;
+    private CancellationTokenSource _cts;
+
+    public string Name => "blocklist";
+
+    public int Count => _snapshot.Count;
+
+    public static void Configure()
+    {
+        ConnectionFilters.Register(new BlocklistFilter());
+    }
+
+    public void Register()
+    {
+        BlocklistConfiguration.Load();
+        var s = BlocklistConfiguration.Settings;
+
+        _path = ResolvePath(s.File);
+        _interval = s.ReloadInterval <= TimeSpan.Zero ? TimeSpan.FromSeconds(60) : s.ReloadInterval;
+        _reportHits = s.ReportHits;
+        _banDuration = s.BanDuration;
+        _suppressionMs = (long)s.PromoteSuppression.TotalMilliseconds;
+    }
+
+    /// <summary>
+    /// Resolves the configured path once: a relative path is anchored to <see cref="Core.BaseDirectory"/>
+    /// (never the process working directory, which differs when the shard is launched from elsewhere), an
+    /// absolute path is taken as-is so several shards can share one generated list.
+    /// </summary>
+    private static string ResolvePath(string configured)
+    {
+        if (string.IsNullOrWhiteSpace(configured))
+        {
+            return null;
+        }
+
+        return Path.IsPathRooted(configured) ? configured : Path.Join(Core.BaseDirectory, configured);
+    }
+
+    public void Start(CancellationToken token)
+    {
+        if (_path == null)
+        {
+            logger.Information("Blocklist disabled (\"file\" empty in blocklist.json)");
+            return;
+        }
+
+        _cts = CancellationTokenSource.CreateLinkedTokenSource(token);
+
+        // A missing file is the shipped default, not an error: the gate stays inert until the poll picks
+        // up whatever the generator first writes. No restart needed.
+        if (File.Exists(_path))
+        {
+            Reload(); // synchronous prime; empty on failure (fail-open)
+        }
+        else
+        {
+            logger.Information("Blocklist inert: no list at \"{Path}\"; polling every {Interval}", _path, _interval);
+        }
+
+        // Sweep the promote-guard so a distinct-IP flood cannot grow it unbounded.
+        Timer.DelayCall(TimeSpan.FromMinutes(1), TimeSpan.FromMinutes(1), SweepGuard);
+
+        _ = Task.Run(() => PollLoop(_cts.Token), _cts.Token);
+    }
+
+    public void Stop()
+    {
+        _cts?.Cancel();
+        _cts?.Dispose();
+        _cts = null;
+    }
+
+    public bool ShouldDeny(IPAddress address)
+    {
+        if (!Evaluate(address, Core.TickCount, out var shouldReport))
+        {
+            return false;
+        }
+
+        if (shouldReport)
+        {
+            // Demand-page this address up to the OS-level bouncer. Enqueue-only; never blocks the loop.
+            BanChannel.Report(address, _banDuration, "blocklist");
+        }
+
+        return true;
+    }
+
+    /// <summary>
+    /// The pure decision, split out so the accept-path policy can be tested without a clock or a ban
+    /// channel. <paramref name="shouldReport"/> is true at most once per suppression window.
+    /// </summary>
+    internal bool Evaluate(IPAddress address, long nowTicks, out bool shouldReport)
+    {
+        shouldReport = false;
+
+        if (!_snapshot.IsBanned(address))
+        {
+            return false;
+        }
+
+        if (_reportHits)
+        {
+            shouldReport = _guard.TryMark(address.ToUInt128(), nowTicks, _suppressionMs);
+        }
+
+        return true;
+    }
+
+    private void SweepGuard() => _guard.Sweep(Core.TickCount);
+
+    // Test hook: inject a snapshot and policy without file I/O.
+    internal void LoadForTesting(BlocklistSnapshot snapshot, bool reportHits = true, long suppressionMs = 60000)
+    {
+        _snapshot = snapshot;
+        _reportHits = reportHits;
+        _suppressionMs = suppressionMs;
+    }
+
+    private async ValueTask PollLoop(CancellationToken token)
+    {
+        while (!token.IsCancellationRequested)
+        {
+            try
+            {
+                await Task.Delay(_interval, token);
+            }
+            catch (OperationCanceledException)
+            {
+                return;
+            }
+
+            try
+            {
+                if (ChangedSinceLastLoad())
+                {
+                    // Parsing millions of lines competes with a save for CPU and page cache, so yield until
+                    // the world is written out. See the threading policy in CLAUDE.md (rules #3 and #10).
+                    while (World.Saving || World.WorldState == WorldState.PendingSave)
+                    {
+                        await Task.Delay(TimeSpan.FromSeconds(1), token);
+                    }
+
+                    Reload();
+                }
+            }
+            catch (OperationCanceledException)
+            {
+                return;
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "Blocklist reload check failed; keeping last snapshot ({Count})", Count);
+            }
+        }
+    }
+
+    private bool ChangedSinceLastLoad()
+    {
+        try
+        {
+            var info = new FileInfo(_path);
+            if (!info.Exists)
+            {
+                return false;
+            }
+
+            if (info.LastWriteTimeUtc == _lastWriteUtc)
+            {
+                return false; // cheapest guard
+            }
+        }
+        catch
+        {
+            return false;
+        }
+
+        return !BlocklistFile.TryReadHeader(_path, out var h) || h.Generated != _lastGenerated;
+    }
+
+    private void Reload()
+    {
+        // Capture the mtime/header BEFORE Load() so the markers describe the version being parsed, not
+        // one the producer swapped in mid-parse. Stale markers only cost an extra reload next poll;
+        // capturing after could skip a version entirely.
+        var writeUtc = default(DateTime);
+        try
+        {
+            writeUtc = new FileInfo(_path).LastWriteTimeUtc;
+        }
+        catch
+        {
+            /* keep default */
+        }
+
+        BlocklistFile.TryReadHeader(_path, out var h);
+
+        var next = BlocklistFile.Load(_path, out var parsed, out var skipped);
+        _snapshot = next; // single volatile swap; readers see old or new whole
+        _lastGenerated = h.Generated;
+        _lastWriteUtc = writeUtc;
+
+        logger.Information("Blocklist loaded {Parsed} entr(ies) ({Count} ranges, {Skipped} skipped) gen={Gen}",
+            parsed, next.Count, skipped, h.Generated);
+    }
+}

Projects/UOContent/Misc/Blocklist/BlocklistSnapshot.cs

@@ -0,0 +1,205 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: BlocklistSnapshot.cs                                            *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Buffers.Text;
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+using Server.Collections;
+
+namespace Server.Network.Bans;
+
+/// <summary>
+/// Immutable dual-stack blocklist. Singles and CIDRs are folded into a single sorted, coalesced
+/// interval index per family: IPv4 as <see cref="uint"/> ranges (lean for the millions-strong common
+/// case), IPv6 as <see cref="UInt128"/> ranges (empty unless the feed carries v6). Immutable → lock-free reads.
+/// </summary>
+public sealed class BlocklistSnapshot
+{
+    public static readonly BlocklistSnapshot Empty = new(SortedRangeIndex<uint>.Empty, SortedRangeIndex<UInt128>.Empty);
+
+    private readonly SortedRangeIndex<uint> _v4;
+    private readonly SortedRangeIndex<UInt128> _v6;
+
+    public int Count => _v4.Count + _v6.Count;
+
+    private BlocklistSnapshot(SortedRangeIndex<uint> v4, SortedRangeIndex<UInt128> v6)
+    {
+        _v4 = v4;
+        _v6 = v6;
+    }
+
+    /// <summary>
+    /// Parses a blocklist directly from its UTF-8/ASCII file bytes — one line at a time, splitting on
+    /// <c>'\n'</c> with no per-line string allocation. IPv4 singles and CIDRs are parsed straight from the
+    /// byte span; IPv6 (the rare path) decodes the single address token and defers to the framework parser.
+    /// Malformed lines increment <paramref name="skipped"/> and never throw. Build-time intermediates use
+    /// the multithreaded pool because this runs off the game loop on the reload/bootstrap thread.
+    /// </summary>
+    public static BlocklistSnapshot Build(ReadOnlySpan<byte> data, out int parsed, out int skipped)
+    {
+        parsed = 0;
+        skipped = 0;
+
+        // Only the two final index arrays (allocated inside SortedRangeIndex.Build) hit the heap; every
+        // build-time buffer here is a pooled ref list. mt: true is required — this runs off the game loop.
+        using var v4 = PooledRefList<SortedRangeIndex<uint>.Range>.Create(mt: true);
+        using var v6 = PooledRefList<SortedRangeIndex<UInt128>.Range>.Create(mt: true);
+
+        var rest = data;
+        while (!rest.IsEmpty)
+        {
+            ReadOnlySpan<byte> line;
+            var nl = rest.IndexOf((byte)'\n');
+            if (nl >= 0)
+            {
+                line = rest[..nl];
+                rest = rest[(nl + 1)..];
+            }
+            else
+            {
+                line = rest;
+                rest = default;
+            }
+
+            line = line[Ascii.Trim(line)];
+            if (line.IsEmpty || line[0] == (byte)'#' || line[0] == (byte)';')
+            {
+                continue;
+            }
+
+            var slash = line.IndexOf((byte)'/');
+            var addr = slash >= 0 ? line[..slash] : line;
+            var bitsToken = slash >= 0 ? line[(slash + 1)..] : default;
+
+            if (addr.IndexOf((byte)':') < 0)
+            {
+                // IPv4 single or CIDR — parsed straight from the byte span.
+                if (slash >= 0)
+                {
+                    if (IPAddressUtility.TryParseV4(addr, out var ip) &&
+                        TryParseBits(bitsToken, out var bits) && bits is >= 0 and <= 32)
+                    {
+                        var size = bits == 0 ? 0xFFFFFFFFu : (1u << (32 - bits)) - 1;
+                        var b = ip & ~size;
+                        v4.Add(new SortedRangeIndex<uint>.Range(b, b + size));
+                        parsed++;
+                    }
+                    else
+                    {
+                        skipped++;
+                    }
+                }
+                else if (IPAddressUtility.TryParseV4(addr, out var ip))
+                {
+                    v4.Add(new SortedRangeIndex<uint>.Range(ip, ip));
+                    parsed++;
+                }
+                else
+                {
+                    skipped++;
+                }
+            }
+            else if (TryDecodeV6(addr, out var v))
+            {
+                // IPv6 is rare in these feeds; the single token was decoded and framework-parsed above.
+                if (slash >= 0)
+                {
+                    if (TryParseBits(bitsToken, out var bits) && bits is >= 0 and <= 128)
+                    {
+                        var mask = bits == 0 ? UInt128.Zero : ~((UInt128.One << (128 - bits)) - 1);
+                        var b = v & mask;
+                        v6.Add(new SortedRangeIndex<UInt128>.Range(b, b | ~mask));
+                        parsed++;
+                    }
+                    else
+                    {
+                        skipped++;
+                    }
+                }
+                else
+                {
+                    v6.Add(new SortedRangeIndex<UInt128>.Range(v, v));
+                    parsed++;
+                }
+            }
+            else
+            {
+                skipped++;
+            }
+        }
+
+        v4.Sort(SortedRangeIndex<uint>.ByMin);
+        v6.Sort(SortedRangeIndex<UInt128>.ByMin);
+        return new BlocklistSnapshot(SortedRangeIndex<uint>.Build(v4.AsSpan()), SortedRangeIndex<UInt128>.Build(v6.AsSpan()));
+    }
+
+    // Decodes a single IPv6 address token from ASCII bytes and validates it via the framework parser.
+    private static bool TryDecodeV6(ReadOnlySpan<byte> addr, out UInt128 v)
+    {
+        v = UInt128.Zero;
+        if (addr.Length > 45)
+        {
+            return false;
+        }
+
+        Span<char> chars = stackalloc char[addr.Length];
+        for (var i = 0; i < addr.Length; i++)
+        {
+            chars[i] = (char)addr[i];
+        }
+
+        if (!IPAddress.TryParse(chars, out var a) || a.AddressFamily != AddressFamily.InterNetworkV6)
+        {
+            return false;
+        }
+
+        v = a.ToUInt128();
+        return true;
+    }
+
+    private static bool TryParseBits(ReadOnlySpan<byte> token, out int bits)
+    {
+        if (Utf8Parser.TryParse(token, out bits, out var consumed) && consumed == token.Length)
+        {
+            return true;
+        }
+
+        bits = 0;
+        return false;
+    }
+
+    public bool IsBanned(IPAddress ip)
+    {
+        if (ip.IsIPv4MappedToIPv6)
+        {
+            // v6-encoded v4 must not dodge the v4 set; extract the embedded v4 uint directly.
+            return IPAddressUtility.TryMappedV4(ip, out var mv) && _v4.Contains(mv);
+        }
+
+        if (ip.AddressFamily == AddressFamily.InterNetwork)
+        {
+            return IPAddressUtility.TryV4(ip, out var v) && _v4.Contains(v);
+        }
+
+        if (ip.AddressFamily == AddressFamily.InterNetworkV6)
+        {
+            return _v6.Contains(ip.ToUInt128());
+        }
+
+        return false;
+    }
+}

Projects/UOContent/Misc/Blocklist/PromotedGuard.cs

@@ -0,0 +1,55 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: PromotedGuard.cs                                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+
+namespace Server.Network.Bans;
+
+/// <summary>Suppresses re-reporting the same IP within a TTL. Accept-path thread only.</summary>
+public sealed class PromotedGuard
+{
+    private readonly Dictionary<UInt128, long> _expiry = [];
+
+    public bool TryMark(UInt128 ip, long nowTicks, long ttlMs)
+    {
+        if (_expiry.TryGetValue(ip, out var exp) && exp - nowTicks > 0)
+        {
+            return false;
+        }
+        _expiry[ip] = nowTicks + ttlMs;
+        return true;
+    }
+
+    public void Sweep(long nowTicks)
+    {
+        if (_expiry.Count == 0)
+        {
+            return;
+        }
+        using var dead = Collections.PooledRefQueue<UInt128>.Create();
+        foreach (var (ip, exp) in _expiry)
+        {
+            if (exp - nowTicks <= 0)
+            {
+                dead.Enqueue(ip);
+            }
+        }
+        while (dead.Count > 0)
+        {
+            _expiry.Remove(dead.Dequeue());
+        }
+    }
+}

Projects/UOContent/Misc/CrowdSec/CrowdSecAlert.cs

@@ -0,0 +1,65 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecAlert.cs                                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Text.Json.Serialization;
+
+namespace Server.Network.Bans.CrowdSec;
+
+/// <summary>One CrowdSec alert (<c>POST /v1/alerts</c> takes an array of these).</summary>
+public sealed class CrowdSecAlert
+{
+    [JsonPropertyName("scenario")] public string Scenario { get; set; }
+    [JsonPropertyName("message")] public string Message { get; set; }
+    [JsonPropertyName("events_count")] public int EventsCount { get; set; } = 1;
+    [JsonPropertyName("start_at")] public string StartAt { get; set; }
+    [JsonPropertyName("stop_at")] public string StopAt { get; set; }
+    [JsonPropertyName("capacity")] public int Capacity { get; set; }
+    [JsonPropertyName("leakspeed")] public string LeakSpeed { get; set; } = "0s";
+    [JsonPropertyName("simulated")] public bool Simulated { get; set; }
+    [JsonPropertyName("events")] public object[] Events { get; set; } = [];
+    [JsonPropertyName("remediation")] public bool Remediation { get; set; } = true;
+    [JsonPropertyName("source")] public CrowdSecSource Source { get; set; }
+    [JsonPropertyName("decisions")] public CrowdSecDecisionDto[] Decisions { get; set; }
+}
+
+public sealed class CrowdSecSource
+{
+    [JsonPropertyName("scope")] public string Scope { get; set; } = "Ip";
+    [JsonPropertyName("value")] public string Value { get; set; }
+}
+
+public sealed class CrowdSecDecisionDto
+{
+    [JsonPropertyName("origin")] public string Origin { get; set; }
+    [JsonPropertyName("type")] public string Type { get; set; } = "ban";
+    [JsonPropertyName("scope")] public string Scope { get; set; } = "Ip";
+    [JsonPropertyName("value")] public string Value { get; set; }
+    [JsonPropertyName("duration")] public string Duration { get; set; }
+    [JsonPropertyName("scenario")] public string Scenario { get; set; }
+}
+
+/// <summary>Watcher login request/response for <c>POST /v1/watchers/login</c>.</summary>
+public sealed class CrowdSecLoginRequest
+{
+    [JsonPropertyName("machine_id")] public string MachineId { get; set; }
+    [JsonPropertyName("password")] public string Password { get; set; }
+}
+
+public sealed class CrowdSecLoginResponse
+{
+    [JsonPropertyName("code")] public int Code { get; set; }
+    [JsonPropertyName("token")] public string Token { get; set; }
+    [JsonPropertyName("expire")] public string Expire { get; set; }
+}

Projects/UOContent/Misc/CrowdSec/CrowdSecAlertClient.cs

@@ -0,0 +1,137 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecAlertClient.cs                                          *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text.Json;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Server.Network.Bans.CrowdSec;
+
+/// <summary>Reporter-side LAPI operations, mockable for tests.</summary>
+public interface ICrowdSecAlertClient : IDisposable
+{
+    ValueTask PostAlertsAsync(IReadOnlyList<CrowdSecAlert> alerts, CancellationToken token);
+    ValueTask DeleteDecisionsAsync(string origin, IPAddress ip, CancellationToken token);
+}
+
+/// <summary>
+/// CrowdSec LAPI watcher client: authenticates with machine credentials and posts/deletes decisions.
+/// Holds a JWT refreshed on expiry or a 401.
+/// </summary>
+public sealed class CrowdSecAlertClient : ICrowdSecAlertClient
+{
+    private static readonly JsonSerializerOptions _jsonOptions = new() { PropertyNameCaseInsensitive = true };
+
+    private readonly HttpClient _http;
+    private readonly string _machineId;
+    private readonly string _password;
+
+    private string _token;
+    private DateTime _tokenExpiresUtc = DateTime.MinValue;
+
+    public CrowdSecAlertClient(CrowdSecSettings settings)
+    {
+        var baseUri = new Uri(settings.LapiUrl, UriKind.Absolute); // fails loud on malformed url
+        _http = new HttpClient { BaseAddress = baseUri, Timeout = TimeSpan.FromSeconds(30) };
+        _http.DefaultRequestHeaders.Add("User-Agent", "ModernUO-watcher/1.0");
+        _machineId = settings.MachineId;
+        _password = settings.Password;
+    }
+
+    private async Task EnsureAuthAsync(CancellationToken token)
+    {
+        if (_token != null && DateTime.UtcNow < _tokenExpiresUtc - TimeSpan.FromMinutes(1))
+        {
+            return;
+        }
+
+        var request = new CrowdSecLoginRequest { MachineId = _machineId, Password = _password };
+        using var response = await _http.PostAsJsonAsync("/v1/watchers/login", request, _jsonOptions, token)
+            .ConfigureAwait(false);
+        response.EnsureSuccessStatusCode();
+
+        var login = await response.Content.ReadFromJsonAsync<CrowdSecLoginResponse>(_jsonOptions, token)
+            .ConfigureAwait(false);
+        _token = login?.Token ?? throw new InvalidOperationException("CrowdSec login returned no token.");
+        _tokenExpiresUtc = DateTime.TryParse(login.Expire, out var exp) ? exp.ToUniversalTime() : DateTime.UtcNow.AddHours(1);
+    }
+
+    private void Authorize(HttpRequestMessage message) =>
+        message.Headers.Authorization = new AuthenticationHeaderValue("Bearer", _token);
+
+    public async ValueTask PostAlertsAsync(IReadOnlyList<CrowdSecAlert> alerts, CancellationToken token)
+    {
+        if (alerts.Count == 0)
+        {
+            return;
+        }
+
+        await SendWithRetryAsync(() =>
+        {
+            var message = new HttpRequestMessage(HttpMethod.Post, "/v1/alerts")
+            {
+                Content = JsonContent.Create(alerts, options: _jsonOptions)
+            };
+            Authorize(message);
+            return message;
+        }, token).ConfigureAwait(false);
+    }
+
+    public async ValueTask DeleteDecisionsAsync(string origin, IPAddress ip, CancellationToken token)
+    {
+        var query = BuildDeleteQuery(origin, ip);
+        await SendWithRetryAsync(() =>
+        {
+            var message = new HttpRequestMessage(HttpMethod.Delete, query);
+            Authorize(message);
+            return message;
+        }, token).ConfigureAwait(false);
+    }
+
+    /// <summary>
+    /// Builds the decisions-delete query string. <paramref name="origin"/> is operator-controlled config
+    /// (crowdsec.json), so it must be escaped like any other untrusted value going into a URL.
+    /// </summary>
+    internal static string BuildDeleteQuery(string origin, IPAddress ip) =>
+        $"/v1/decisions?origin={Uri.EscapeDataString(origin)}&ip={Uri.EscapeDataString(ip.ToString())}";
+
+    private async ValueTask SendWithRetryAsync(Func<HttpRequestMessage> build, CancellationToken token)
+    {
+        await EnsureAuthAsync(token).ConfigureAwait(false);
+
+        using var first = build();
+        using var response = await _http.SendAsync(first, token).ConfigureAwait(false);
+        if (response.StatusCode != HttpStatusCode.Unauthorized)
+        {
+            response.EnsureSuccessStatusCode();
+            return;
+        }
+
+        // Token rejected mid-flight: force a re-login and retry once.
+        _token = null;
+        await EnsureAuthAsync(token).ConfigureAwait(false);
+        using var retry = build();
+        using var retryResponse = await _http.SendAsync(retry, token).ConfigureAwait(false);
+        retryResponse.EnsureSuccessStatusCode();
+    }
+
+    public void Dispose() => _http.Dispose();
+}

Projects/UOContent/Misc/CrowdSec/CrowdSecConfiguration.cs

@@ -0,0 +1,101 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecConfiguration.cs                                        *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.IO;
+using System.Text.Json.Serialization;
+using Server.Json;
+
+namespace Server.Network.Bans.CrowdSec;
+
+/// <summary>
+/// Loads the <see cref="CrowdSecSettings"/> from <c>Configuration/crowdsec.json</c> (matching the
+/// per-feature JSON config pattern used by <c>AssistantConfiguration</c>). Loaded once; a missing file
+/// writes a disabled-by-default template so operators have something to edit.
+/// </summary>
+public static class CrowdSecConfiguration
+{
+    private const string _path = "Configuration/crowdsec.json";
+
+    public static CrowdSecSettings Settings { get; private set; }
+
+    public static void Load()
+    {
+        var path = Path.Join(Core.BaseDirectory, _path);
+
+        if (File.Exists(path))
+        {
+            Settings = JsonConfig.Deserialize<CrowdSecSettings>(path);
+        }
+        else
+        {
+            Settings = new CrowdSecSettings
+            {
+                LapiUrl = "http://127.0.0.1:8080",
+                MachineId = "",
+                Password = "",
+                Origin = "modernuo",
+                ManualBanDuration = TimeSpan.FromHours(168),
+                FlushInterval = TimeSpan.FromSeconds(1),
+                MaxQueue = 10000
+            };
+
+            Save();
+        }
+    }
+
+    private static void Save()
+    {
+        JsonConfig.Serialize(Path.Join(Core.BaseDirectory, _path), Settings);
+    }
+}
+
+/// <summary>
+/// Bound configuration for <see cref="CrowdSecReporter"/>. Read once at <c>Configure()</c>.
+/// The reporter is inert unless <see cref="ReportingEnabled"/> is true.
+/// </summary>
+public record CrowdSecSettings
+{
+    /// <summary>LAPI endpoint. Default <c>http://127.0.0.1:8080</c>.</summary>
+    [JsonPropertyName("lapiUrl")]
+    public string LapiUrl { get; set; } = "http://127.0.0.1:8080";
+
+    /// <summary>Watcher machine id from <c>cscli machines add</c>. Empty disables reporting.</summary>
+    [JsonPropertyName("machineId")]
+    public string MachineId { get; set; } = "";
+
+    /// <summary>Watcher password paired with <see cref="MachineId"/>.</summary>
+    [JsonPropertyName("password")]
+    public string Password { get; set; } = "";
+
+    /// <summary>Decision <c>origin</c> stamped on our contributions. Default <c>modernuo</c>.</summary>
+    [JsonPropertyName("origin")]
+    public string Origin { get; set; } = "modernuo";
+
+    /// <summary>Duration for manual admin bans pushed to CrowdSec. Default 168h (renewable). Finite so a missed retract self-heals.</summary>
+    [JsonPropertyName("manualBanDuration")]
+    public TimeSpan ManualBanDuration { get; set; } = TimeSpan.FromHours(168);
+
+    /// <summary>Max time the drain coalesces before flushing a batch. Default 1s.</summary>
+    [JsonPropertyName("flushInterval")]
+    public TimeSpan FlushInterval { get; set; } = TimeSpan.FromSeconds(1);
+
+    /// <summary>Bounded contribution queue capacity; overflow is dropped (counted). Default 10000.</summary>
+    [JsonPropertyName("maxQueue")]
+    public int MaxQueue { get; set; } = 10000;
+
+    [JsonIgnore]
+    public bool ReportingEnabled => !string.IsNullOrWhiteSpace(MachineId) && !string.IsNullOrWhiteSpace(Password);
+}

Projects/UOContent/Misc/CrowdSec/CrowdSecReporter.cs

@@ -0,0 +1,399 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: CrowdSecReporter.cs                                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Collections.Generic;
+using System.Net;
+using System.Threading;
+using System.Threading.Channels;
+using System.Threading.Tasks;
+using Server.Logging;
+
+namespace Server.Network.Bans.CrowdSec;
+
+/// <summary>
+/// Contributes locally-decided bans to CrowdSec via the LAPI alerts API. Non-blocking on the accept
+/// path: <see cref="Report"/> enqueues onto a bounded, drop-on-overflow channel drained by a single
+/// background task that coalesces by IP and POSTs batched alerts.
+/// </summary>
+public sealed class CrowdSecReporter : IBanReporter
+{
+    private static readonly ILogger logger = LogFactory.GetLogger(typeof(CrowdSecReporter));
+
+    internal readonly record struct ReportItem(IPAddress Ip, TimeSpan Ttl, string Reason, bool Retract);
+
+    // Bounded retry for transient LAPI failures during a drain send (network blips, 5xx). Distinct from
+    // CrowdSecAlertClient.SendWithRetryAsync's single 401-relogin retry, which is an auth concern.
+    private static readonly TimeSpan[] _retryDelays = [TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(2)];
+
+    private ICrowdSecAlertClient _client;
+    private CrowdSecSettings _settings;
+    private Channel<ReportItem> _queue;
+    private CancellationTokenSource _cts;
+    private Task _drainTask;
+    private int _dropped;
+    private int _sendFailures;
+
+    public CrowdSecReporter()
+    {
+    }
+
+    // Test/embedding ctor with an injected client + settings.
+    internal CrowdSecReporter(ICrowdSecAlertClient client, CrowdSecSettings settings)
+    {
+        _client = client;
+        _settings = settings;
+        _queue = CreateQueue(settings.MaxQueue);
+    }
+
+    public string Name => "crowdsec";
+    public bool CanRetract => true;
+    public int DroppedCount => _dropped;
+
+    /// <summary>
+    /// Batches ultimately dropped after the bounded transient-retry in <see cref="DrainLoop"/> gave up.
+    /// Distinct from <see cref="DroppedCount"/> (queue-overflow drops on the accept path): this counts
+    /// sustained LAPI outages so operators can see contribution loss instead of it being silent.
+    /// </summary>
+    public int SendFailureCount => _sendFailures;
+
+    /// <summary>The drain loop's task, so tests can assert it stays alive until the loop exits.</summary>
+    internal Task DrainTaskForTesting => _drainTask;
+
+    public static void Configure()
+    {
+        BanChannel.Register(new CrowdSecReporter());
+    }
+
+    public void Register()
+    {
+        CrowdSecConfiguration.Load();
+        _settings ??= CrowdSecConfiguration.Settings;
+    }
+
+    public void Start(CancellationToken token)
+    {
+        if (!_settings.ReportingEnabled)
+        {
+            logger.Information("CrowdSec reporter disabled (machineId/password empty in crowdsec.json)");
+            return;
+        }
+
+        _client ??= new CrowdSecAlertClient(_settings);
+        _queue ??= CreateQueue(_settings.MaxQueue);
+        _cts = CancellationTokenSource.CreateLinkedTokenSource(token);
+        _drainTask = Task.Run(() => DrainLoop(_cts.Token), _cts.Token);
+    }
+
+    public void Stop()
+    {
+        _cts?.Cancel();
+
+        // The flush below reads a SingleReader channel, so wait for the drain to actually exit first.
+        var drainExited = true;
+        try
+        {
+            // Wait(timeout) is false only on timeout; a throw means faulted/cancelled, which is still exited.
+            drainExited = _drainTask == null || _drainTask.Wait(TimeSpan.FromSeconds(2));
+        }
+        catch
+        {
+            // Ignored: a faulted wait means the drain has completed and released the channel.
+        }
+
+        _cts?.Dispose();
+        _cts = null;
+
+        if (drainExited)
+        {
+            FlushRemainingOnStop();
+        }
+
+        _client?.Dispose();
+        _drainTask = null;
+    }
+
+    /// <summary>
+    /// Best-effort bounded flush of whatever is still queued at shutdown. Blocking is correct here — the
+    /// loop has stopped ticking — but must not happen on the loop thread: <see cref="Stop"/> runs where
+    /// <c>SynchronizationContext.Current</c> is the <c>EventLoopContext</c>, and a captured continuation
+    /// would be posted to a queue nothing pumps any more. <see cref="Task.Run(Func{Task})"/> keeps the
+    /// chain on the pool; the bounded wait caps a wedged send at a few seconds of shutdown.
+    /// </summary>
+    private void FlushRemainingOnStop()
+    {
+        if (_queue == null || _client == null)
+        {
+            return;
+        }
+
+        _queue.Writer.TryComplete();
+
+        List<ReportItem> reports = [];
+        List<ReportItem> retracts = [];
+        while (_queue.Reader.TryRead(out var item))
+        {
+            (item.Retract ? retracts : reports).Add(item);
+        }
+
+        if (reports.Count == 0 && retracts.Count == 0)
+        {
+            return;
+        }
+
+        try
+        {
+            if (!Task.Run(() => FlushRemainingOnStopAsync(reports, retracts)).Wait(TimeSpan.FromSeconds(4)))
+            {
+                logger.Warning(
+                    "CrowdSec flush-on-stop timed out; {Count} item(s) not contributed",
+                    reports.Count + retracts.Count
+                );
+            }
+        }
+        catch (Exception e)
+        {
+            logger.Warning(e, "CrowdSec flush-on-stop failed");
+        }
+    }
+
+    /// <summary>
+    /// Uses a fresh token, not the drain loop's already-cancelled one, which would fail every send
+    /// immediately. Reports go as one deduped batch; retracts go as individual DELETEs so an admin's
+    /// unban propagates on a clean shutdown. Leftovers self-heal via
+    /// <see cref="CrowdSecSettings.ManualBanDuration"/>.
+    /// </summary>
+    private async Task FlushRemainingOnStopAsync(List<ReportItem> reports, List<ReportItem> retracts)
+    {
+        using var flushCts = new CancellationTokenSource(TimeSpan.FromSeconds(3));
+
+        if (reports.Count > 0)
+        {
+            var alerts = BuildAlerts(reports, _settings, DateTime.UtcNow);
+            try
+            {
+                await _client.PostAlertsAsync(alerts, flushCts.Token).ConfigureAwait(false);
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "CrowdSec flush-on-stop reports failed");
+                RecordSendFailure(alerts.Count);
+            }
+        }
+
+        HashSet<string> seen = [];
+        for (var i = 0; i < retracts.Count; i++)
+        {
+            if (flushCts.IsCancellationRequested)
+            {
+                break; // out of budget; the rest self-heal via ManualBanDuration
+            }
+
+            var ip = retracts[i].Ip;
+            if (!seen.Add(ip.ToString()))
+            {
+                continue;
+            }
+
+            try
+            {
+                await _client.DeleteDecisionsAsync(_settings.Origin, ip, flushCts.Token).ConfigureAwait(false);
+            }
+            catch (Exception e)
+            {
+                logger.Warning(e, "CrowdSec flush-on-stop retract failed for {Address}", ip);
+                RecordSendFailure(1);
+            }
+        }
+    }
+
+    public void Report(IPAddress address, TimeSpan ttl, string reason) =>
+        Enqueue(new ReportItem(address, ttl, reason, false));
+
+    public void Retract(IPAddress address) =>
+        Enqueue(new ReportItem(address, TimeSpan.Zero, "retract", true));
+
+    private void Enqueue(ReportItem item)
+    {
+        if (_queue == null || !_queue.Writer.TryWrite(item))
+        {
+            Interlocked.Increment(ref _dropped);
+        }
+    }
+
+    // FullMode.Wait (the default) makes TryWrite return false immediately when the channel is full
+    // instead of blocking the caller — exactly the non-blocking drop-on-overflow behavior the accept
+    // path requires. DropWrite would silently discard the new item and always report success, which
+    // would make overflow undetectable.
+    private static Channel<ReportItem> CreateQueue(int capacity) =>
+        Channel.CreateBounded<ReportItem>(new BoundedChannelOptions(Math.Max(1, capacity))
+        {
+            FullMode = BoundedChannelFullMode.Wait,
+            SingleReader = true
+        });
+
+    // Must return Task: Start() passes this to Task.Run, which has no Func<ValueTask> overload, so a
+    // ValueTask would bind to Task.Run<TResult> and yield a Task<ValueTask> that completes at the first
+    // await rather than when the loop exits.
+    private async Task DrainLoop(CancellationToken token)
+    {
+        var reader = _queue.Reader;
+
+        while (!token.IsCancellationRequested)
+        {
+            try
+            {
+                if (!await reader.WaitToReadAsync(token).ConfigureAwait(false))
+                {
+                    return;
+                }
+
+                // Coalesce a burst before flushing.
+                await Task.Delay(_settings.FlushInterval, token).ConfigureAwait(false);
+
+                List<ReportItem> reports = [];
+                List<ReportItem> retracts = [];
+                while (reader.TryRead(out var item))
+                {
+                    (item.Retract ? retracts : reports).Add(item);
+                }
+
+                if (reports.Count > 0)
+                {
+                    var alerts = BuildAlerts(reports, _settings, DateTime.UtcNow);
+                    if (!await SendWithBoundedRetryAsync(() => _client.PostAlertsAsync(alerts, token), token)
+                            .ConfigureAwait(false))
+                    {
+                        RecordSendFailure(alerts.Count);
+                    }
+                }
+
+                for (var i = 0; i < retracts.Count; i++)
+                {
+                    var ip = retracts[i].Ip;
+                    if (!await SendWithBoundedRetryAsync(() => _client.DeleteDecisionsAsync(_settings.Origin, ip, token), token)
+                            .ConfigureAwait(false))
+                    {
+                        RecordSendFailure(1);
+                    }
+                }
+            }
+            catch (OperationCanceledException)
+            {
+                return;
+            }
+            catch (Exception e)
+            {
+                // Contribution is auxiliary: log and keep draining. Never crash the shard.
+                logger.Warning(e, "CrowdSec contribution flush failed; dropped this batch");
+            }
+        }
+    }
+
+    /// <summary>
+    /// Sends with up to 3 attempts total (1 initial + 2 retries), backing off 1s then 2s between
+    /// attempts, for transient LAPI failures (network blips, 5xx). Backoff uses <see cref="Task.Delay"/>
+    /// so it never blocks the thread; a cancellation during backoff propagates as
+    /// <see cref="OperationCanceledException"/> so the drain loop exits cleanly. Returns false (never
+    /// throws for a send failure) once attempts are exhausted, so the caller can count the drop and keep
+    /// draining instead of losing the rest of the batch/queue.
+    /// </summary>
+    private static async ValueTask<bool> SendWithBoundedRetryAsync(Func<ValueTask> send, CancellationToken token)
+    {
+        for (var attempt = 0; ; attempt++)
+        {
+            try
+            {
+                await send().ConfigureAwait(false);
+                return true;
+            }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
+            catch (Exception e)
+            {
+                if (attempt >= _retryDelays.Length)
+                {
+                    logger.Warning(e, "CrowdSec send failed after {Attempts} attempt(s); giving up", attempt + 1);
+                    return false;
+                }
+
+                var delay = _retryDelays[attempt];
+                logger.Warning(e, "CrowdSec send failed (attempt {Attempt}); retrying in {Delay}", attempt + 1, delay);
+                await Task.Delay(delay, token).ConfigureAwait(false);
+            }
+        }
+    }
+
+    private void RecordSendFailure(int itemCount)
+    {
+        var total = Interlocked.Increment(ref _sendFailures);
+        logger.Warning(
+            "CrowdSec contribution batch dropped after retries ({Items} item(s)); total dropped batches: {Total}",
+            itemCount,
+            total
+        );
+    }
+
+    /// <summary>Coalesces items by IP (last write wins) and builds one alert per unique address.</summary>
+    internal static List<CrowdSecAlert> BuildAlerts(IEnumerable<ReportItem> items, CrowdSecSettings settings, DateTime nowUtc)
+    {
+        Dictionary<string, ReportItem> byIp = [];
+        foreach (var item in items)
+        {
+            byIp[item.Ip.ToString()] = item;
+        }
+
+        var timestamp = nowUtc.ToString("yyyy-MM-ddTHH:mm:ss.fffZ");
+        var alerts = new List<CrowdSecAlert>(byIp.Count);
+
+        foreach (var (value, item) in byIp)
+        {
+            var ttl = item.Reason == "manual" || item.Ttl <= TimeSpan.Zero ? settings.ManualBanDuration : item.Ttl;
+            var scenario = $"{settings.Origin}/{item.Reason}";
+
+            alerts.Add(new CrowdSecAlert
+            {
+                Scenario = scenario,
+                Message = $"ModernUO {item.Reason} ban for {value}",
+                StartAt = timestamp,
+                StopAt = timestamp,
+                Source = new CrowdSecSource { Scope = "Ip", Value = value },
+                Decisions =
+                [
+                    new CrowdSecDecisionDto
+                    {
+                        Origin = settings.Origin,
+                        Type = "ban",
+                        Scope = "Ip",
+                        Value = value,
+                        Duration = FormatDuration(ttl),
+                        Scenario = scenario
+                    }
+                ]
+            });
+        }
+
+        return alerts;
+    }
+
+    /// <summary>CrowdSec accepts Go durations; whole seconds are unambiguous and sufficient.</summary>
+    internal static string FormatDuration(TimeSpan ttl)
+    {
+        var seconds = (long)ttl.TotalSeconds;
+        return $"{Math.Max(1, seconds)}s";
+    }
+}

Projects/UOContent/Misc/Firewall/CidrFirewallEntry.cs

@@ -25,8 +25,15 @@ public class CidrFirewallEntry : BaseFirewallEntry
     public override UInt128 MaxIpAddress { get; }
 
     public CidrFirewallEntry(string ipAddressOrCidr)
-        : this(ParseIPAddress(ipAddressOrCidr, out var prefixLength), prefixLength)
     {
+        // Core owns the CIDR -> normalized range parse.
+        if (!IPAddressUtility.TryParseCidrRange(ipAddressOrCidr, out var min, out var max))
+        {
+            throw new ArgumentException("Invalid IP address or CIDR.", nameof(ipAddressOrCidr));
+        }
+
+        MinIpAddress = min;
+        MaxIpAddress = max;
     }
 
     public CidrFirewallEntry(IPAddress minAddress, IPAddress maxAddress)
@@ -50,26 +57,4 @@ public class CidrFirewallEntry : BaseFirewallEntry
         MaxIpAddress = Utility.CreateCidrAddress(bytes, prefixLength, true);
     }
 
-    private static IPAddress ParseIPAddress(ReadOnlySpan<char> ipString, out int prefixLength)
-    {
-        var slashIndex = ipString.IndexOf('/');
-        var ipAddress = IPAddress.Parse(slashIndex > -1 ? ipString[..slashIndex] : ipString);
-        var maxPrefixLength = ipAddress.AddressFamily == AddressFamily.InterNetworkV6 ? 128 : 32;
-
-        if (slashIndex == -1)
-        {
-            prefixLength = maxPrefixLength;
-        }
-        else
-        {
-            var prefixPart = ipString[(slashIndex + 1)..];
-
-            if (!int.TryParse(prefixPart, out prefixLength) || prefixLength < 0 || prefixLength > maxPrefixLength)
-            {
-                throw new ArgumentException("Invalid prefix length.");
-            }
-        }
-
-        return ipAddress;
-    }
 }

Projects/UOContent/Misc/Firewall/Firewall.cs

@@ -0,0 +1,413 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: Firewall.cs                                                     *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Buffers;
+using System.Collections.Generic;
+using System.IO;
+using System.Net;
+using System.Runtime.CompilerServices;
+using Server.Collections;
+using Server.Json;
+using Server.Logging;
+
+namespace Server.Network;
+
+public static class Firewall
+{
+    // Single-threaded: the accept path, admin gump/command, TTL expiry timer, and boot load all run on
+    // the main game loop. No locks, caches, or version counters are needed. See the ban-channel design doc.
+    // _entries is the authoritative store (gump/persistence/TTL/command all work against it); _index is a
+    // derived, rebuild-on-demand SortedRangeIndex used only for the accept-path IsBlocked lookup, shared
+    // with the same sorted-range binary-search primitive the blocklist uses (see BlocklistSnapshot).
+    private static readonly List<IFirewallEntry> _entries = [];
+
+    // Entries with a TTL: entry -> absolute expiry tick (Core.TickCount). Permanent entries are absent.
+    private static readonly Dictionary<IFirewallEntry, long> _expiring = [];
+
+    private static SortedRangeIndex<UInt128> _index = SortedRangeIndex<UInt128>.Empty;
+    private static bool _indexDirty;
+
+    private static readonly ILogger logger = LogFactory.GetLogger(typeof(Firewall));
+    private const string _path = "Configuration/firewall.json";
+    private const string _legacyPath = "firewall.cfg";
+    private static bool _dirty;
+    private static bool _configured;
+
+    public static int FirewallSetCount => _entries.Count;
+
+    public static void ReadFirewallSet(Action<IReadOnlyCollection<IFirewallEntry>> callback) => callback(_entries);
+
+    public static bool IsBlocked(IPAddress address)
+    {
+        if (_entries.Count == 0)
+        {
+            return false;
+        }
+
+        EnsureIndex();
+        return _index.Contains(address.ToUInt128());
+    }
+
+    // Rebuilds the derived lookup index from the authoritative _entries list, but only when entries have
+    // changed since the last build. Runs on the main game loop, so the pooled build buffer is single-threaded
+    // (mt: false); only the two final SortedRangeIndex arrays are heap-allocated.
+    private static void EnsureIndex()
+    {
+        if (!_indexDirty)
+        {
+            return;
+        }
+
+        using var ranges = PooledRefList<SortedRangeIndex<UInt128>.Range>.Create(_entries.Count, mt: false);
+        for (var i = 0; i < _entries.Count; i++)
+        {
+            var entry = _entries[i];
+            ranges.Add(new SortedRangeIndex<UInt128>.Range(entry.MinIpAddress, entry.MaxIpAddress));
+        }
+
+        ranges.Sort(SortedRangeIndex<UInt128>.ByMin);
+        _index = SortedRangeIndex<UInt128>.Build(ranges.AsSpan());
+        _indexDirty = false;
+    }
+
+    public static bool Add(IFirewallEntry firewallEntry) => Add(firewallEntry, TimeSpan.Zero);
+
+    /// <summary>
+    /// Adds an entry. <paramref name="ttl"/> &lt;= <see cref="TimeSpan.Zero"/> means permanent. Returns false
+    /// if the entry was already present.
+    /// </summary>
+    // Indexed scan (no closure allocation); firewall lists are small, so O(n) is negligible and this
+    // stays off the hot path (Add/Remove are admin/boot actions, not the accept path).
+    private static int IndexOfEntry(IFirewallEntry entry)
+    {
+        for (var i = 0; i < _entries.Count; i++)
+        {
+            if (_entries[i].CompareTo(entry) == 0)
+            {
+                return i;
+            }
+        }
+
+        return -1;
+    }
+
+    public static bool Add(IFirewallEntry firewallEntry, TimeSpan ttl, bool persist = true)
+    {
+        if (firewallEntry == null || IndexOfEntry(firewallEntry) >= 0)
+        {
+            return false;
+        }
+
+        _entries.Add(firewallEntry);
+
+        if (ttl > TimeSpan.Zero)
+        {
+            _expiring[firewallEntry] = Core.TickCount + (long)ttl.TotalMilliseconds;
+        }
+
+        _indexDirty = true;
+
+        if (persist)
+        {
+            MarkDirty();
+        }
+
+        return true;
+    }
+
+    public static bool Remove(IFirewallEntry entry)
+    {
+        if (entry == null)
+        {
+            return false;
+        }
+
+        var index = IndexOfEntry(entry);
+        if (index < 0)
+        {
+            return false;
+        }
+
+        // Remove the stored instance from _expiring (not the passed reference), so a value-equal
+        // entry created elsewhere still clears the TTL bookkeeping.
+        var stored = _entries[index];
+        _entries.RemoveAt(index);
+        _expiring.Remove(stored);
+        _indexDirty = true;
+        MarkDirty();
+        return true;
+    }
+
+    /// <summary>
+    /// Removes every entry whose TTL has elapsed. Called from the main-thread maintenance timer (Task 2).
+    /// </summary>
+    internal static void ExpireEntries(long nowTicks)
+    {
+        if (_expiring.Count == 0)
+        {
+            return;
+        }
+
+        List<IFirewallEntry> expired = null;
+        foreach (var (entry, expiresAt) in _expiring)
+        {
+            if (expiresAt - nowTicks <= 0)
+            {
+                (expired ??= []).Add(entry);
+            }
+        }
+
+        if (expired == null)
+        {
+            return;
+        }
+
+        for (var i = 0; i < expired.Count; i++)
+        {
+            var entry = expired[i];
+            _entries.Remove(entry);
+            _expiring.Remove(entry);
+        }
+
+        _indexDirty = true;
+        MarkDirty();
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static IFirewallEntry ToFirewallEntry(object entry) =>
+        entry switch
+        {
+            IFirewallEntry firewallEntry => firewallEntry,
+            IPAddress address            => new SingleIpFirewallEntry(address),
+            string s                     => ToFirewallEntry(s),
+            _                            => null
+        };
+
+    public static IFirewallEntry ToFirewallEntry(string entry)
+    {
+        if (entry == null)
+        {
+            return null;
+        }
+
+        try
+        {
+            var rangeSeparator = entry.IndexOf('-');
+            if (rangeSeparator > -1)
+            {
+                return new CidrFirewallEntry(
+                    IPAddress.Parse(entry.AsSpan(0, rangeSeparator)),
+                    IPAddress.Parse(entry.AsSpan(rangeSeparator + 1))
+                );
+            }
+
+            if (entry.IndexOf('/') > -1)
+            {
+                return new CidrFirewallEntry(entry);
+            }
+
+            return new SingleIpFirewallEntry(entry);
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    public static void Configure()
+    {
+        if (_configured)
+        {
+            return;
+        }
+        _configured = true;
+
+        var path = Path.Join(Core.BaseDirectory, _path);
+
+        if (File.Exists(path))
+        {
+            LoadFrom(JsonConfig.Deserialize<FirewallSettings>(path));
+        }
+        else
+        {
+            var legacyPath = ResolveLegacyCfgPath();
+            if (legacyPath != null)
+            {
+                MigrateLegacyCfg(legacyPath);
+                Save(); // materialize firewall.json; the .cfg is no longer read after this
+                TryMarkLegacyCfgMigrated(legacyPath);
+            }
+        }
+
+        // Main-thread maintenance: expire TTLs and flush pending writes. No background thread.
+        Timer.DelayCall(TimeSpan.FromSeconds(30), TimeSpan.FromSeconds(30), Maintenance);
+
+        // Expose the set to the accept path. Everything else (gump, commands, persistence) keeps using
+        // the Firewall API directly; only the per-connection question goes through the filter registry.
+        ConnectionFilters.Register(FirewallConnectionFilter.Instance);
+    }
+
+    private static void Maintenance()
+    {
+        ExpireEntries(Core.TickCount);
+
+        if (_dirty)
+        {
+            Save();
+        }
+    }
+
+    private static void MarkDirty() => _dirty = true;
+
+    internal static void LoadFrom(FirewallSettings settings)
+    {
+        if (settings?.Entries == null)
+        {
+            return;
+        }
+
+        // Core.Now: this runs on the game loop, via the Configure sweep.
+        var now = Core.Now;
+        var records = settings.Entries;
+        for (var i = 0; i < records.Length; i++)
+        {
+            var record = records[i];
+            var entry = ToFirewallEntry(record.Value);
+            if (entry == null)
+            {
+                logger.Warning("Ignoring unparseable firewall entry \"{Entry}\"", record.Value);
+                continue;
+            }
+
+            var ttl = TimeSpan.Zero;
+            if (record.Expires is { } expires)
+            {
+                ttl = expires - now;
+                if (ttl <= TimeSpan.Zero)
+                {
+                    continue; // already expired
+                }
+            }
+
+            Add(entry, ttl, persist: false);
+        }
+    }
+
+    internal static FirewallSettings ToSettings()
+    {
+        // expires is derived below as now + (expiresAtTick - nowTicks), so both operands must come from
+        // the same instant. Core.Now and Core.TickCount are refreshed together each loop iteration; a
+        // fresh DateTime.UtcNow here would bake the loop's lag into every persisted expiry.
+        var now = Core.Now;
+        var nowTicks = Core.TickCount;
+        var list = new List<FirewallEntryRecord>(_entries.Count);
+
+        for (var i = 0; i < _entries.Count; i++)
+        {
+            var entry = _entries[i];
+            DateTime? expires = null;
+            if (_expiring.TryGetValue(entry, out var expiresAtTick))
+            {
+                expires = now.AddMilliseconds(expiresAtTick - nowTicks);
+            }
+
+            list.Add(new FirewallEntryRecord { Value = entry.ToString(), Expires = expires });
+        }
+
+        return new FirewallSettings { Entries = list.ToArray() };
+    }
+
+    public static void Save()
+    {
+        _dirty = false;
+        var path = Path.Join(Core.BaseDirectory, _path);
+        var tmp = $"{path}.tmp";
+        JsonConfig.Serialize(tmp, ToSettings());
+        File.Move(tmp, path, overwrite: true); // atomic swap
+    }
+
+    /// <summary>
+    /// Locates the legacy firewall.cfg to migrate. The modern convention is <see cref="Core.BaseDirectory"/>,
+    /// checked first; the pre-collapse <c>AdminFirewall</c> used a bare relative path (resolved against the
+    /// process's current working directory), which may differ from <see cref="Core.BaseDirectory"/> when the
+    /// shard is launched from elsewhere, so that's checked as a fallback. Returns null if neither exists.
+    /// </summary>
+    private static string ResolveLegacyCfgPath()
+    {
+        var underBaseDirectory = Path.Join(Core.BaseDirectory, _legacyPath);
+        if (File.Exists(underBaseDirectory))
+        {
+            return underBaseDirectory;
+        }
+
+        return File.Exists(_legacyPath) ? _legacyPath : null;
+    }
+
+    private static void MigrateLegacyCfg(string legacyPath)
+    {
+        var searchValues = SearchValues.Create("*Xx?");
+
+        using var reader = new StreamReader(legacyPath);
+        while (reader.ReadLine() is { } line)
+        {
+            line = line.Trim();
+            if (line.Length == 0)
+            {
+                continue;
+            }
+
+            if (line.AsSpan().ContainsAny(searchValues))
+            {
+                logger.Warning("Legacy firewall entry \"{Entry}\" ignored during migration", line);
+                continue;
+            }
+
+            var entry = ToFirewallEntry(line);
+            if (entry != null)
+            {
+                Add(entry, TimeSpan.Zero, persist: false);
+            }
+        }
+
+        logger.Information("Migrated {Count} entr(ies) from legacy firewall.cfg to firewall.json", _entries.Count);
+    }
+
+    /// <summary>
+    /// Renames the migrated <c>.cfg</c> to <c>firewall.cfg.migrated</c> so it isn't re-scanned on the next
+    /// boot and operators can see it was already migrated. Best-effort: a locked/read-only file must not
+    /// fail startup, since the migration itself (firewall.json) already succeeded.
+    /// </summary>
+    private static void TryMarkLegacyCfgMigrated(string legacyPath)
+    {
+        try
+        {
+            File.Move(legacyPath, $"{legacyPath}.migrated", overwrite: true);
+        }
+        catch (Exception e)
+        {
+            logger.Warning(e, "Could not rename migrated legacy firewall file \"{Path}\"", legacyPath);
+        }
+    }
+
+    internal static void ResetForTesting()
+    {
+        _entries.Clear();
+        _expiring.Clear();
+        _index = SortedRangeIndex<UInt128>.Empty;
+        _indexDirty = false;
+        _configured = false;
+    }
+}

Projects/UOContent/Misc/Firewall/FirewallConnectionFilter.cs

@@ -0,0 +1,52 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: FirewallConnectionFilter.cs                                     *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System.Net;
+using System.Threading;
+
+namespace Server.Network;
+
+/// <summary>
+/// Exposes the admin-curated <see cref="Firewall"/> set to the accept path as an
+/// <see cref="IConnectionFilter"/>. The firewall keeps its own API (the admin gump and commands mutate
+/// it directly); this is only the accept-path adapter, since a static class cannot implement an
+/// interface. It is the cheapest gate to consult — an empty set costs one length compare — so
+/// <see cref="Firewall.Configure"/> registers it first.
+/// </summary>
+internal sealed class FirewallConnectionFilter : IConnectionFilter
+{
+    public static readonly FirewallConnectionFilter Instance = new();
+
+    private FirewallConnectionFilter()
+    {
+    }
+
+    public string Name => "firewall";
+
+    // Firewall.Configure() owns loading and registration.
+    public void Register()
+    {
+    }
+
+    // Nothing to hydrate: the set loads at Configure and is maintained by a main-loop timer.
+    public void Start(CancellationToken token)
+    {
+    }
+
+    /// <summary>Flushes pending writes on the way down so a TTL expiry or late admin edit is not lost.</summary>
+    public void Stop() => Firewall.Save();
+
+    public bool ShouldDeny(IPAddress address) => Firewall.IsBlocked(address);
+}

Projects/UOContent/Misc/Firewall/FirewallSettings.cs

@@ -0,0 +1,42 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2026 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: FirewallSettings.cs                                             *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+using System.Text.Json.Serialization;
+
+namespace Server.Network;
+
+/// <summary>
+/// Persisted local firewall entries (manual admin bans). Stored at <c>Configuration/firewall.json</c>.
+/// Auto-detected rate-limit trips are never persisted — they are contributed to CrowdSec, not stored here.
+/// </summary>
+public record FirewallSettings
+{
+    [JsonPropertyName("entries")]
+    public FirewallEntryRecord[] Entries { get; set; } = [];
+}
+
+/// <summary>
+/// One persisted entry. <see cref="Value"/> is a single IP, a <c>min-max</c> range, or CIDR.
+/// <see cref="Expires"/> is UTC wall-clock; null means permanent.
+/// </summary>
+public record FirewallEntryRecord
+{
+    [JsonPropertyName("value")]
+    public string Value { get; set; }
+
+    [JsonPropertyName("expires")]
+    public DateTime? Expires { get; set; }
+}