Merge #11

Add rate limiting

README.md

@@ -46,6 +46,49 @@ It is also recommended to [set up a Reverse Proxy](https://empostor.github.io/ge
 4. Press "Open in Among Us". Among Us should open.
 5. Your server should appear in the regions list!
 
+## Configuration
+
+All settings live in `config.json` next to the server binary (a full sample is [`src/Empostor.Server/config.json`](src/Empostor.Server/config.json)). Unknown keys are ignored, so an old config keeps working after an update.
+
+| Section | Purpose |
+| --- | --- |
+| `Server` | Public IP/port, listen address and the dynamic (delta) UDP port range `DeltaPortStart`..`DeltaPortEnd` |
+| `HttpServer` | Web API, admin panel and matchmaking token endpoint (`Enabled`, `ListenIp`, `ListenPort`) |
+| `AntiCheat` | Server-side anticheat, including the [IP request rate limit](#ip-request-rate-limit) |
+| `Timeout` | Spawn and connection timeouts |
+| `Compatibility` | Game version compatibility rules |
+| `Debug` | Game recorder |
+| `AuthApi` | Friend code resolution (`Mode`: `GameServices`, `Ume`, `Both` or `Off`) |
+| `Admin` | Admin panel password and marketplace URL |
+| `HPLP` | HPLP public region listing |
+
+### AntiCheat
+
+| Key | Default | Description |
+| --- | --- | --- |
+| `Enabled` | `true` | Master switch of the anticheat |
+| `BanIpFromGame` | `true` | Also block banned IPs on the game (UDP) side |
+| `AllowCheatingHosts` | `Never` | What happens to hosts that cheat |
+| `EnableGameFlowChecks`, `EnableMustBeHostChecks`, `EnableOwnershipChecks`, `EnableRoleChecks`, `EnableTargetChecks` | `true` | Game flow / state validation |
+| `EnableColorLimitChecks`, `EnableNameLimitChecks`, `EnableItemLimitChecks` | `true` | Lobby limits (colors, names, items) |
+| `ForbidProtocolExtensions` | `true` | Reject unknown/extension protocol messages |
+| `EnablePacketSizeChecks`, `PacketSizeLimit` | `true`, `1203` | Maximum inbound packet size |
+| `EnableIpRateLimit` | `true` | IP request rate limit (below) |
+| `IpRateLimitRequests` | `30` | Max TCP (HTTP) requests per IP per window, `0` disables the limit |
+| `IpRateLimitWindowMinutes` | `5` | Length of the rate limit window in minutes |
+
+#### Ip request rate limit
+
+Within one window (5 minutes by default) the same IP may only make `IpRateLimitRequests` (default `30`) TCP (HTTP) requests — this protects the HTTP API against connection/request flooding. When the limit is exceeded:
+
+- Every normal endpoint answers with `429 Too Many Requests` and a localized hint, chosen from the request's `Accept-Language` header, e.g. `请求过于频繁请 5 分钟后重试`. The `Retry-After` header says how many seconds are left.
+- `POST /api/user` **and** `PUT`/`GET /api/games` (the whole join flow of the game client: matchmaking token + FindHost) are **never rejected over HTTP** — failing them there would only leave the client on a black screen, which just logs `CoSendRequest failed` and hangs. Both still count against the quota, and while an IP is over quota the server also skips the outbound friend code API calls (a cached/fallback code is used instead) so the endpoint cannot be abused for amplification. To keep a flooding IP from draining the dynamic port range, such joins are **not given a pool port**: they all receive the same shared *reject port*, a single pre-bound UDP socket whose only job is to answer the handshake with the localized hint in the client's own language (`请求过于频繁请 5 分钟后重试`) and close it again — the player is told why they cannot join instead of seeing a black screen, and only one socket is used no matter how many requests arrive. `GamesController` echoes the token's port back, so the client is naturally sent to that reject port. In fixed-port mode (`DeltaPortStart=0`) the main port is used instead.
+- `/admin` and `/api/admin` are neither counted nor limited, so the dashboard can never lock the operator out.
+
+The message lives under the key `ratelimit.too_frequent` in `Languages/*.json` (and in the built-in defaults in `LanguageService.cs`), so you can reword or translate it there. Set `IpRateLimitRequests` to `0` to turn the whole feature off.
+
+Empostor usually runs behind a CDN or reverse proxy, so the real client IP is taken from the `X-Real-IP` header, then from the first entry of `X-Forwarded-For`, and only afterwards from the socket address. Make sure your CDN/proxy forwards one of these headers — otherwise every player would share the proxy IP's quota. Note that the game client polls some endpoints (e.g. `/api/games`) while you play: if `30` per 5 minutes is too tight for your players, raise `IpRateLimitRequests` (for example to `120`).
+
 ## Contributing
 Please read the [contributing guidelines](https://github.com/Empostor/Empostor/blob/main/CONTRIBUTING.md).
 

src/Empostor.Api/Config/AntiCheatConfig.cs

@@ -33,5 +33,11 @@ namespace Empostor.Api.Config
         public bool EnablePacketSizeChecks { get; set; } = true;
 
         public int PacketSizeLimit { get; set; } = 1203;
+
+        public bool EnableIpRateLimit { get; set; } = true;
+
+        public int IpRateLimitRequests { get; set; } = 30;
+
+        public int IpRateLimitWindowMinutes { get; set; } = 5;
     }
 }

src/Empostor.Api/Languages/LanguageService.cs

@@ -155,6 +155,7 @@ public sealed class LanguageService
     // Any Pr fix grammer wrongs is OK!
     private const string DefaultEn = """
 {
+  "ratelimit.too_frequent": "Too many requests, please try again in {0} minute(s).",
   "command.error": "An error occurred while executing #{0}.",
   "command.usage": "Usage: #{0}",
   "command.help.list": "=== Commands ===",
@@ -215,6 +216,7 @@ public sealed class LanguageService
 
     private const string DefaultZhCn = """
 {
+  "ratelimit.too_frequent": "请求过于频繁请 {0} 分钟后重试",
   "command.error": "执行 #{0}时发生错误。",
   "command.usage": "用法：#{0}",
   "command.help.list": "=== 指令列表 ===",
@@ -275,6 +277,7 @@ public sealed class LanguageService
 
     private const string DefaultZhTw = """
 {
+  "ratelimit.too_frequent": "請求過於頻繁請 {0} 分鐘後重試",
   "command.error": "執行 #{0}時發生錯誤。",
   "command.usage": "用法：#{0}",
   "command.help.list": "=== 指令列表 ===",
@@ -335,6 +338,7 @@ public sealed class LanguageService
 
     private const string DefaultKo = """
 {
+  "ratelimit.too_frequent": "요청이 너무 많습니다. {0}분 후에 다시 시도해 주세요.",
   "command.error": "#{0}실행 중 오류가 발생했습니다.",
   "command.usage": "사용법: #{0}",
   "command.help.list": "=== 명령어 목록 ===",
@@ -381,6 +385,7 @@ public sealed class LanguageService
 
     private const string DefaultRu = """
 {
+  "ratelimit.too_frequent": "Слишком много запросов, повторите попытку через {0} мин.",
   "command.error": "Ошибка при выполнении #{0}.",
   "command.usage": "Использование: #{0}",
   "command.help.list": "=== Команды ===",
@@ -427,6 +432,7 @@ public sealed class LanguageService
 
     private const string DefaultDe = """
 {
+  "ratelimit.too_frequent": "Zu viele Anfragen, bitte versuche es in {0} Minute(n) erneut.",
   "command.error": "Fehler beim Ausführen von #{0}.",
   "command.usage": "Verwendung: #{0}",
   "command.help.list": "=== Befehle ===",
@@ -473,6 +479,7 @@ public sealed class LanguageService
 
     private const string DefaultFr = """
 {
+  "ratelimit.too_frequent": "Trop de requêtes, veuillez réessayer dans {0} minute(s).",
   "command.error": "Erreur lors de l'exécution de #{0}.",
   "command.usage": "Utilisation : #{0}",
   "command.help.list": "=== Commandes ===",
@@ -519,6 +526,7 @@ public sealed class LanguageService
 
     private const string DefaultJa = """
 {
+  "ratelimit.too_frequent": "リクエストが多すぎます。{0}分後に再試行してください。",
   "command.error": "#{0}の実行中にエラーが発生しました。",
   "command.usage": "使い方：#{0}",
   "command.help.list": "=== コマンド一覧 ===",
@@ -565,6 +573,7 @@ public sealed class LanguageService
 
     private const string DefaultPt = """
 {
+  "ratelimit.too_frequent": "Muitos pedidos, tente novamente em {0} minuto(s).",
   "command.error": "Ocorreu um erro ao executar #{0}.",
   "command.usage": "Uso: #{0}",
   "command.help.list": "=== Comandos ===",
@@ -611,6 +620,7 @@ public sealed class LanguageService
 
     private const string DefaultPtBr = """
 {
+  "ratelimit.too_frequent": "Muitas solicitações, tente novamente em {0} minuto(s).",
   "command.error": "Ocorreu um erro ao executar #{0}.",
   "command.usage": "Uso: #{0}",
   "command.help.list": "=== Comandos ===",
@@ -655,6 +665,7 @@ public sealed class LanguageService
 
     private const string DefaultEs = """
 {
+  "ratelimit.too_frequent": "Demasiadas solicitudes, inténtalo de nuevo en {0} minuto(s).",
   "command.error": "Error al ejecutar #{0}.",
   "command.usage": "Uso: #{0}",
   "command.help.list": "=== Comandos ===",
@@ -699,6 +710,7 @@ public sealed class LanguageService
 
     private const string DefaultIt = """
 {
+  "ratelimit.too_frequent": "Troppe richieste, riprova tra {0} minuto/i.",
   "command.error": "Errore durante l'esecuzione di #{0}.",
   "command.usage": "Utilizzo: #{0}",
   "command.help.list": "=== Comandi ===",
@@ -743,6 +755,7 @@ public sealed class LanguageService
 
     private const string DefaultNl = """
 {
+  "ratelimit.too_frequent": "Te veel verzoeken, probeer het over {0} minuut/minuten opnieuw.",
   "command.error": "Fout bij uitvoeren van #{0}.",
   "command.usage": "Gebruik: #{0}",
   "command.help.list": "=== Commando's ===",
@@ -787,6 +800,7 @@ public sealed class LanguageService
 
     private const string DefaultFil = """
 {
+  "ratelimit.too_frequent": "Masyaraming request, subukan muli sa {0} minuto.",
   "command.error": "May error sa pagpapatakbo ng #{0}.",
   "command.usage": "Paggamit: #{0}",
   "command.help.list": "=== Mga Command ===",
@@ -831,6 +845,7 @@ public sealed class LanguageService
 
     private const string DefaultGa = """
 {
+  "ratelimit.too_frequent": "Iarraidh ró-mhóra, bain triail eile as i {0} nóiméad.",
   "command.error": "Earráid agus #{0}á rith.",
   "command.usage": "Úsáid: #{0}",
   "command.help.list": "=== Orduithe ===",

src/Empostor.Server/Http/AdminController.cs

@@ -750,31 +750,12 @@ namespace Empostor.Server.Http
 
         private IPAddress? GetClientIp()
         {
-            // Check reverse-proxy headers first so we get the real client IP,
+            // CDN / reverse proxy headers first so we get the real client IP,
             // not the CDN/nginx IP. Using Connection.RemoteIpAddress directly
             // would rate-limit or ban the proxy instead of the actual user.
-            var xRealIp = HttpContext.Request.Headers["X-Real-IP"].FirstOrDefault();
-            if (!string.IsNullOrEmpty(xRealIp) && IPAddress.TryParse(xRealIp, out var realIp))
-            {
-                return Normalize(realIp);
-            }
-
-            var xForwardedFor = HttpContext.Request.Headers["X-Forwarded-For"].FirstOrDefault();
-            if (!string.IsNullOrEmpty(xForwardedFor))
-            {
-                var first = xForwardedFor.Split(',')[0].Trim();
-                if (IPAddress.TryParse(first, out var fwdIp))
-                {
-                    return Normalize(fwdIp);
-                }
-            }
-
-            return Normalize(HttpContext.Connection.RemoteIpAddress);
+            return RealIpResolver.Resolve(HttpContext);
         }
 
-        private static IPAddress? Normalize(IPAddress? ip)
-            => ip?.IsIPv4MappedToIPv6 == true ? ip.MapToIPv4() : ip;
-
         private static object Err(string msg) => new { error = msg };
 
         private static string Fmt(TimeSpan t)

src/Empostor.Server/Http/IpRateLimitMiddleware.cs

@@ -0,0 +1,160 @@
+using System;
+using System.Globalization;
+using System.Text.Encodings.Web;
+using System.Text.Json;
+using System.Threading.Tasks;
+using Empostor.Api.Languages;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Logging;
+
+namespace Empostor.Server.Http;
+
+// Anticheat "Ip request rate limit": rejects TCP (HTTP) requests of IPs that
+// exceeded the configured quota and answers with a localized hint.
+public sealed class IpRateLimitMiddleware
+{
+    private const string MessageKey = IpRateLimitService.MessageKey;
+
+    private static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
+
+        Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
+    };
+
+    private readonly RequestDelegate _next;
+    private readonly IpRateLimitService _rateLimit;
+    private readonly LanguageService _language;
+    private readonly ILogger<IpRateLimitMiddleware> _logger;
+
+    public IpRateLimitMiddleware(
+        RequestDelegate next,
+        IpRateLimitService rateLimit,
+        LanguageService language,
+        ILogger<IpRateLimitMiddleware> logger)
+    {
+        _next = next;
+        _rateLimit = rateLimit;
+        _language = language;
+        _logger = logger;
+    }
+
+    public async Task InvokeAsync(HttpContext context)
+    {
+        // The admin panel polls its own endpoints, so it neither consumes the
+        // quota nor is ever rate-limited.
+        if (IsAdminPath(context.Request.Path))
+        {
+            await _next(context);
+            return;
+        }
+
+        var ip = RealIpResolver.Resolve(context);
+
+        // Always counted, so the join endpoint cannot be used to burn through
+        // the quota without being noticed.
+        var overQuota = !_rateLimit.TryRegister(ip, out var retryAfter);
+
+        // The join flow of the game client (POST /api/user, then
+        // PUT/GET /api/games for FindHost) must never fail over HTTP: the
+        // client only logs such a failure and then hangs on a black screen.
+        // These endpoints are therefore counted but never blocked — over-quota
+        // players still take no pool port and no outbound auth call, and are
+        // pointed at one shared reject port whose listener sends the localized
+        // hint in-game (see TokenController / Matchmaker).
+        if (!overQuota || IsGameFlowPath(context.Request.Path))
+        {
+            await _next(context);
+            return;
+        }
+
+        var minutes = IpRateLimitService.MinutesUntilRetry(retryAfter);
+
+        var message = _language
+            .Get(MessageKey, ResolveLangCode(context))
+            .Format(minutes)
+            .Get();
+
+        _logger.LogWarning(
+            "IpRateLimit blocked {Ip} on {Path} │ retry in {Minutes}m",
+            ip?.ToString() ?? "unknown",
+            context.Request.Path.Value ?? "/",
+            minutes);
+
+        context.Response.StatusCode = StatusCodes.Status429TooManyRequests;
+        context.Response.Headers["Retry-After"] =
+            ((int)Math.Ceiling(retryAfter.TotalSeconds)).ToString(CultureInfo.InvariantCulture);
+        context.Response.ContentType = "application/json; charset=utf-8";
+        await context.Response.WriteAsync(JsonSerializer.Serialize(new { error = message }, JsonOptions));
+    }
+
+    // The admin panel polls its own endpoints, so it is never rate-limited.
+    private static bool IsAdminPath(PathString path)
+        => path.StartsWithSegments("/admin", StringComparison.OrdinalIgnoreCase)
+           || path.StartsWithSegments("/api/admin", StringComparison.OrdinalIgnoreCase);
+
+    // The join flow of the game client: matchmaking token + FindHost.
+    // GamesController echoes the token's port back, so the reject port handed
+    // out by /api/user is what the client connects to.
+    private static bool IsGameFlowPath(PathString path)
+        => path.StartsWithSegments("/api/user", StringComparison.OrdinalIgnoreCase)
+           || path.StartsWithSegments("/api/games", StringComparison.OrdinalIgnoreCase);
+
+    private static string ResolveLangCode(HttpContext context)
+    {
+        var acceptLanguage = context.Request.Headers["Accept-Language"].ToString();
+        foreach (var entry in acceptLanguage.Split(','))
+        {
+            var tag = entry.Split(';')[0].Trim();
+            if (tag.Length == 0 || tag == "*")
+            {
+                continue;
+            }
+
+            var code = MapLangTag(tag);
+            if (code != null)
+            {
+                return code;
+            }
+        }
+
+        return "en";
+    }
+
+    // Maps a browser/client language tag (zh-CN, pt-BR, ...) to one of the
+    // server's Languages/*.json codes.
+    private static string? MapLangTag(string tag)
+    {
+        var lower = tag.ToLowerInvariant();
+
+        if (lower.StartsWith("zh", StringComparison.Ordinal))
+        {
+            return lower.Contains("hant", StringComparison.Ordinal)
+                   || lower.Contains("tw", StringComparison.Ordinal)
+                   || lower.Contains("hk", StringComparison.Ordinal)
+                   || lower.Contains("mo", StringComparison.Ordinal)
+                ? "zh_TW"
+                : "zh_CN";
+        }
+
+        if (lower.StartsWith("pt-br", StringComparison.Ordinal))
+        {
+            return "pt_BR";
+        }
+
+        if (lower.StartsWith("fil", StringComparison.Ordinal) || lower.StartsWith("tl", StringComparison.Ordinal))
+        {
+            return "fil";
+        }
+
+        foreach (var code in new[] { "en", "es", "pt", "ko", "ru", "nl", "fr", "de", "it", "ja", "ga" })
+        {
+            if (lower.StartsWith(code, StringComparison.Ordinal))
+            {
+                return code;
+            }
+        }
+
+        return null;
+    }
+}

src/Empostor.Server/Http/IpRateLimitService.cs

@@ -0,0 +1,157 @@
+using System;
+using System.Collections.Concurrent;
+using System.Net;
+using Empostor.Api.Config;
+using Microsoft.Extensions.Options;
+
+namespace Empostor.Server.Http;
+
+// Per-IP request counter used by the anticheat "Ip request rate limit".
+// Every real IP gets a fixed window (default 5 minutes); when the IP sends
+// more TCP (HTTP) requests than configured (default 30) it is blocked until
+// the window slides away.
+public sealed class IpRateLimitService
+{
+    // Language key of the localized hint, see Languages/*.json.
+    public const string MessageKey = "ratelimit.too_frequent";
+
+    private static readonly TimeSpan CleanupInterval = TimeSpan.FromSeconds(60);
+
+    private readonly IOptions<AntiCheatConfig> _options;
+    private readonly ConcurrentDictionary<string, Window> _windows = new();
+    private DateTime _lastCleanupUtc = DateTime.MinValue;
+
+    public IpRateLimitService(IOptions<AntiCheatConfig> options)
+    {
+        _options = options;
+    }
+
+    // Counts the request against the IP. Returns false when the IP exhausted
+    // its quota; retryAfter then tells how long the caller still has to wait.
+    public bool TryRegister(IPAddress? ip, out TimeSpan retryAfter)
+    {
+        retryAfter = TimeSpan.Zero;
+
+        var config = _options.Value;
+        var window = GetWindow(config);
+        if (ip == null || window == null || config.IpRateLimitRequests <= 0)
+        {
+            return true;
+        }
+
+        var value = window.Value;
+        Cleanup(value);
+
+        var now = DateTime.UtcNow;
+        var entry = _windows.GetOrAdd(ip.ToString(), _ => new Window(now));
+
+        lock (entry)
+        {
+            if (now - entry.StartUtc >= value)
+            {
+                entry.StartUtc = now;
+                entry.Count = 0;
+            }
+
+            entry.Count++;
+            if (entry.Count <= config.IpRateLimitRequests)
+            {
+                return true;
+            }
+
+            // Blocked requests do not restart the window, so the lockout ends
+            // at most one full window after the first request of the burst.
+            retryAfter = entry.StartUtc + value - now;
+            if (retryAfter < TimeSpan.Zero)
+            {
+                retryAfter = TimeSpan.Zero;
+            }
+
+            return false;
+        }
+    }
+
+    // Reads the quota without counting a request — used to answer the client
+    // in-game (and to skip expensive work) when the IP is already over quota.
+    public bool IsLimited(IPAddress? ip, out TimeSpan retryAfter)
+    {
+        retryAfter = TimeSpan.Zero;
+
+        var config = _options.Value;
+        var window = GetWindow(config);
+        if (ip == null || window == null || config.IpRateLimitRequests <= 0)
+        {
+            return false;
+        }
+
+        if (!_windows.TryGetValue(ip.ToString(), out var entry))
+        {
+            return false;
+        }
+
+        var now = DateTime.UtcNow;
+        lock (entry)
+        {
+            if (now - entry.StartUtc >= window.Value || entry.Count <= config.IpRateLimitRequests)
+            {
+                return false;
+            }
+
+            retryAfter = entry.StartUtc + window.Value - now;
+            if (retryAfter < TimeSpan.Zero)
+            {
+                retryAfter = TimeSpan.Zero;
+            }
+
+            return true;
+        }
+    }
+
+    private static TimeSpan? GetWindow(AntiCheatConfig config)
+    {
+        if (!config.EnableIpRateLimit)
+        {
+            return null;
+        }
+
+        return TimeSpan.FromMinutes(Math.Max(1, config.IpRateLimitWindowMinutes));
+    }
+
+    // Whole minutes to wait, always at least one so the hint never says
+    // "please try again in 0 minutes".
+    public static int MinutesUntilRetry(TimeSpan retryAfter)
+    {
+        var minutes = (int)Math.Ceiling(retryAfter.TotalMinutes);
+        return minutes < 1 ? 1 : minutes;
+    }
+
+    private void Cleanup(TimeSpan window)
+    {
+        var now = DateTime.UtcNow;
+        if (now - _lastCleanupUtc < CleanupInterval)
+        {
+            return;
+        }
+
+        _lastCleanupUtc = now;
+        foreach (var pair in _windows)
+        {
+            if (now - pair.Value.StartUtc > window + CleanupInterval)
+            {
+                _windows.TryRemove(pair.Key, out _);
+            }
+        }
+    }
+
+    private sealed class Window
+    {
+        public Window(DateTime startUtc)
+        {
+            StartUtc = startUtc;
+        }
+
+        public DateTime StartUtc { get; set; }
+
+        public int Count { get; set; }
+    }
+}

src/Empostor.Server/Http/RealIpResolver.cs

@@ -0,0 +1,36 @@
+using System.Linq;
+using System.Net;
+using Microsoft.AspNetCore.Http;
+
+namespace Empostor.Server.Http;
+
+// Resolves the real client IP of an HTTP (TCP) request.
+// Behind a CDN / reverse proxy Connection.RemoteIpAddress is the proxy's
+// address, so the forwarding headers are checked first — otherwise rate
+// limiting or banning would hit the CDN node instead of the actual user.
+public static class RealIpResolver
+{
+    public static IPAddress? Resolve(HttpContext context)
+    {
+        var xRealIp = context.Request.Headers["X-Real-IP"].FirstOrDefault();
+        if (!string.IsNullOrEmpty(xRealIp) && IPAddress.TryParse(xRealIp, out var realIp))
+        {
+            return Normalize(realIp);
+        }
+
+        var xForwardedFor = context.Request.Headers["X-Forwarded-For"].FirstOrDefault();
+        if (!string.IsNullOrEmpty(xForwardedFor))
+        {
+            var first = xForwardedFor.Split(',')[0].Trim();
+            if (IPAddress.TryParse(first, out var forwardedIp))
+            {
+                return Normalize(forwardedIp);
+            }
+        }
+
+        return Normalize(context.Connection.RemoteIpAddress);
+    }
+
+    private static IPAddress? Normalize(IPAddress? ip)
+        => ip?.IsIPv4MappedToIPv6 == true ? ip.MapToIPv4() : ip;
+}

src/Empostor.Server/Http/TokenController.cs

@@ -36,6 +36,7 @@ public sealed class TokenController : ControllerBase
     private readonly AuthApiConfig _authApiConfig;
     private readonly PortPoolService _portPool;
     private readonly IDeltaListenerManager _deltaListenerManager;
+    private readonly IpRateLimitService _rateLimit;
 
     public TokenController(
         ILogger<TokenController> logger,
@@ -43,7 +44,8 @@ public sealed class TokenController : ControllerBase
         AuthCacheService authCache,
         IOptions<AuthApiConfig> authApiConfig,
         PortPoolService portPool,
-        IDeltaListenerManager deltaListenerManager)
+        IDeltaListenerManager deltaListenerManager,
+        IpRateLimitService rateLimit)
     {
         _logger = logger;
         _httpClientFactory = httpClientFactory;
@@ -51,6 +53,7 @@ public sealed class TokenController : ControllerBase
         _authApiConfig = authApiConfig.Value;
         _portPool = portPool;
         _deltaListenerManager = deltaListenerManager;
+        _rateLimit = rateLimit;
     }
 
     [HttpPost]
@@ -74,9 +77,44 @@ public sealed class TokenController : ControllerBase
                 return Unauthorized(new { error = "Invalid token content" });
             }
 
-            var friendCode = await GetFriendCodeAsync(eosToken, productUserId);
-            var matchmakerToken = GenerateMatchmakerToken(productUserId);
             var clientIp = GetClientIp();
+            var friendCode = await GetFriendCodeAsync(eosToken, productUserId, clientIp);
+            var matchmakerToken = GenerateMatchmakerToken(productUserId);
+
+            // Over quota: never take a pool port for a join that cannot succeed
+            // — one port per blocked request would let a single IP drain the
+            // whole delta range. The client is pointed at the shared reject
+            // port instead, whose listener answers with the localized hint: no
+            // game, no black screen, one socket. Port 0 (fixed-port mode) means
+            // the main port, which rejects it the same way.
+            if (_rateLimit.IsLimited(clientIp, out var joinRetryAfter))
+            {
+                var rejectPort = await _deltaListenerManager.GetRateLimitRejectPortAsync();
+                if (rejectPort > 0 || !_portPool.IsEnabled)
+                {
+                    _logger.LogWarning(
+                        "TokenUser {Puid} {Ip} over the request rate limit, sent to reject port {Port} (retry in {Seconds}s).",
+                        productUserId, clientIp, rejectPort,
+                        (int)Math.Ceiling(joinRetryAfter.TotalSeconds));
+
+                    return Ok(Convert.ToBase64String(JsonSerializer.SerializeToUtf8Bytes(new TokenResponse
+                    {
+                        Content = new TokenContent
+                        {
+                            ProductUserId = productUserId,
+                            FriendCode = friendCode,
+                        },
+                        Hash = matchmakerToken,
+                        Port = rejectPort,
+                    })));
+                }
+
+                // No reject port available (pool exhausted): fall through to
+                // the normal path, which has its own full/exhausted handling.
+                _logger.LogWarning(
+                    "TokenUser {Puid} {Ip} over the request rate limit but no reject port available, falling back to a normal port.",
+                    productUserId, clientIp);
+            }
 
             _authCache.Store(productUserId, matchmakerToken, friendCode, clientIp);
 
@@ -175,32 +213,14 @@ public sealed class TokenController : ControllerBase
 
     private IPAddress? GetClientIp()
     {
-        var xRealIp = HttpContext.Request.Headers["X-Real-IP"].FirstOrDefault();
-        if (!string.IsNullOrEmpty(xRealIp) && IPAddress.TryParse(xRealIp, out var realIp))
-        {
-            return Normalize(realIp);
-        }
-
-        var xForwardedFor = HttpContext.Request.Headers["X-Forwarded-For"].FirstOrDefault();
-        if (!string.IsNullOrEmpty(xForwardedFor))
-        {
-            var first = xForwardedFor.Split(',')[0].Trim();
-            if (IPAddress.TryParse(first, out var fwdIp))
-            {
-                return Normalize(fwdIp);
-            }
-        }
-
-        return Normalize(HttpContext.Connection.RemoteIpAddress);
+        // CDN / reverse proxy aware: X-Real-IP / X-Forwarded-For first.
+        return RealIpResolver.Resolve(HttpContext);
     }
 
-    private static IPAddress? Normalize(IPAddress? ip)
-        => ip?.IsIPv4MappedToIPv6 == true ? ip.MapToIPv4() : ip;
-
     private static string NormalizeIpString(IPAddress? ip)
         => ip?.IsIPv4MappedToIPv6 == true ? ip.MapToIPv4().ToString() : ip?.ToString() ?? "unknown";
 
-    private async Task<string> GetFriendCodeAsync(string eosToken, string productUserId)
+    private async Task<string> GetFriendCodeAsync(string eosToken, string productUserId, IPAddress? clientIp)
     {
         var cached = TryGetFriendCodeFromCache(productUserId);
         if (cached != null)
@@ -211,6 +231,17 @@ public sealed class TokenController : ControllerBase
             return cached;
         }
 
+        // The join request is never rejected because of the Ip rate limit (the
+        // player is told in-game instead), so skip the outbound auth calls
+        // here — otherwise an IP could keep amplifying traffic to us.
+        if (_rateLimit.IsLimited(clientIp, out _))
+        {
+            _logger.LogWarning(
+                "TokenControllerFriendCode skipped for PUID={Puid}: {Ip} is over the request rate limit, using fallback",
+                productUserId, clientIp);
+            return GenerateFallbackFriendCode(productUserId);
+        }
+
         var mode = _authApiConfig.Mode;
         _logger.LogDebug("TokenControllerAuthApi mode: {Mode}", mode);
 

src/Empostor.Server/Languages/de.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "Grund: {0}",
   "ban.notice.unban": "Entbannungszeit: {0}",
   "ban.notice.unban_permanent": "Entbannungszeit: Dauerhaft",
-  "ban.notice.contact": "Bei Fragen wende dich an den Administrator."
+  "ban.notice.contact": "Bei Fragen wende dich an den Administrator.",
+  "ratelimit.too_frequent": "Zu viele Anfragen, bitte versuche es in {0} Minute(n) erneut."
 }

src/Empostor.Server/Languages/en.json

@@ -70,5 +70,6 @@
   "ban.notice.reason": "Reason: {0}",
   "ban.notice.unban": "Unban time: {0}",
   "ban.notice.unban_permanent": "Unban time: Permanent",
-  "ban.notice.contact": "If you have any questions, please contact the administrator."
+  "ban.notice.contact": "If you have any questions, please contact the administrator.",
+  "ratelimit.too_frequent": "Too many requests, please try again in {0} minute(s)."
 }

src/Empostor.Server/Languages/es.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Motivo: {0}",
   "ban.notice.unban": "Fin del baneo: {0}",
   "ban.notice.unban_permanent": "Fin del baneo: Permanente",
-  "ban.notice.contact": "Si tienes dudas, contacta con un administrador."
+  "ban.notice.contact": "Si tienes dudas, contacta con un administrador.",
+  "ratelimit.too_frequent": "Demasiadas solicitudes, inténtalo de nuevo en {0} minuto(s)."
 }

src/Empostor.Server/Languages/fil.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Dahilan: {0}",
   "ban.notice.unban": "Oras ng pag-unban: {0}",
   "ban.notice.unban_permanent": "Oras ng pag-unban: Permanente",
-  "ban.notice.contact": "Kung may tanong, makipag-ugnayan sa administrator."
+  "ban.notice.contact": "Kung may tanong, makipag-ugnayan sa administrator.",
+  "ratelimit.too_frequent": "Masyaraming request, subukan muli sa {0} minuto."
 }

src/Empostor.Server/Languages/fr.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "Raison : {0}",
   "ban.notice.unban": "Débannissement : {0}",
   "ban.notice.unban_permanent": "Débannissement : Permanent",
-  "ban.notice.contact": "En cas de question, contactez un administrateur."
+  "ban.notice.contact": "En cas de question, contactez un administrateur.",
+  "ratelimit.too_frequent": "Trop de requêtes, veuillez réessayer dans {0} minute(s)."
 }

src/Empostor.Server/Languages/ga.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Cúis: {0}",
   "ban.notice.unban": "Am dí-chosc: {0}",
   "ban.notice.unban_permanent": "Am dí-chosc: Buan",
-  "ban.notice.contact": "Má tá ceist agat, déan teagmháil le riarthóir."
+  "ban.notice.contact": "Má tá ceist agat, déan teagmháil le riarthóir.",
+  "ratelimit.too_frequent": "Iarraidh ró-mhóra, bain triail eile as i {0} nóiméad."
 }

src/Empostor.Server/Languages/it.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Motivo: {0}",
   "ban.notice.unban": "Sbanno: {0}",
   "ban.notice.unban_permanent": "Sbanno: Permanente",
-  "ban.notice.contact": "Per qualsiasi domanda, contatta l'amministratore."
+  "ban.notice.contact": "Per qualsiasi domanda, contatta l'amministratore.",
+  "ratelimit.too_frequent": "Troppe richieste, riprova tra {0} minuto/i."
 }

src/Empostor.Server/Languages/ja.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "理由：{0}",
   "ban.notice.unban": "BAN解除日時：{0}",
   "ban.notice.unban_permanent": "BAN解除日時：永久",
-  "ban.notice.contact": "ご不明な点があれば管理者にお問い合わせください。"
+  "ban.notice.contact": "ご不明な点があれば管理者にお問い合わせください。",
+  "ratelimit.too_frequent": "リクエストが多すぎます。{0}分後に再試行してください。"
 }

src/Empostor.Server/Languages/ko.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "사유: {0}",
   "ban.notice.unban": "차단 해제 시간: {0}",
   "ban.notice.unban_permanent": "차단 해제 시간: 영구",
-  "ban.notice.contact": "문의 사항이 있으면 관리자에게 연락해 주세요."
+  "ban.notice.contact": "문의 사항이 있으면 관리자에게 연락해 주세요.",
+  "ratelimit.too_frequent": "요청이 너무 많습니다. {0}분 후에 다시 시도해 주세요."
 }

src/Empostor.Server/Languages/nl.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Reden: {0}",
   "ban.notice.unban": "Ontbantijd: {0}",
   "ban.notice.unban_permanent": "Ontbantijd: Permanent",
-  "ban.notice.contact": "Neem bij vragen contact op met de beheerder."
+  "ban.notice.contact": "Neem bij vragen contact op met de beheerder.",
+  "ratelimit.too_frequent": "Te veel verzoeken, probeer het over {0} minuut/minuten opnieuw."
 }

src/Empostor.Server/Languages/pt.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "Motivo: {0}",
   "ban.notice.unban": "Desbanimento: {0}",
   "ban.notice.unban_permanent": "Desbanimento: Permanente",
-  "ban.notice.contact": "Em caso de dúvidas, contacte o administrador."
+  "ban.notice.contact": "Em caso de dúvidas, contacte o administrador.",
+  "ratelimit.too_frequent": "Muitos pedidos, tente novamente em {0} minuto(s)."
 }

src/Empostor.Server/Languages/pt_BR.json

@@ -37,5 +37,6 @@
   "ban.notice.reason": "Motivo: {0}",
   "ban.notice.unban": "Desbanimento: {0}",
   "ban.notice.unban_permanent": "Desbanimento: Permanente",
-  "ban.notice.contact": "Em caso de dúvidas, contate o administrador."
+  "ban.notice.contact": "Em caso de dúvidas, contate o administrador.",
+  "ratelimit.too_frequent": "Muitas solicitações, tente novamente em {0} minuto(s)."
 }

src/Empostor.Server/Languages/ru.json

@@ -39,5 +39,6 @@
   "ban.notice.reason": "Причина: {0}",
   "ban.notice.unban": "Время разбана: {0}",
   "ban.notice.unban_permanent": "Время разбана: навсегда",
-  "ban.notice.contact": "Если у вас есть вопросы, обратитесь к администратору."
+  "ban.notice.contact": "Если у вас есть вопросы, обратитесь к администратору.",
+  "ratelimit.too_frequent": "Слишком много запросов, повторите попытку через {0} мин."
 }

src/Empostor.Server/Languages/zh_CN.json

@@ -70,5 +70,6 @@
   "ban.notice.reason": "理由：{0}",
   "ban.notice.unban": "解封时间：{0}",
   "ban.notice.unban_permanent": "解封时间：永久",
-  "ban.notice.contact": "如有问题请联系管理员"
+  "ban.notice.contact": "如有问题请联系管理员",
+  "ratelimit.too_frequent": "请求过于频繁请 {0} 分钟后重试"
 }

src/Empostor.Server/Languages/zh_TW.json

@@ -53,5 +53,6 @@
   "ban.notice.reason": "理由：{0}",
   "ban.notice.unban": "解封時間：{0}",
   "ban.notice.unban_permanent": "解封時間：永久",
-  "ban.notice.contact": "如有問題請聯絡管理員"
+  "ban.notice.contact": "如有問題請聯絡管理員",
+  "ratelimit.too_frequent": "請求過於頻繁請 {0} 分鐘後重試"
 }

src/Empostor.Server/Net/IDeltaListenerManager.cs

@@ -18,4 +18,13 @@ public interface IDeltaListenerManager
     ///     Stops and disposes the UDP listener on a specific port.
     /// </summary>
     ValueTask StopDeltaListenerAsync(int port);
+
+    /// <summary>
+    ///     Returns the single shared UDP port that rate-limited (over-quota) join
+    ///     requests are pointed at, binding it on first use. Its listener never
+    ///     creates a player, it only sends the localized "too frequent" hint, so
+    ///     an over-quota IP cannot consume a pool port per request.
+    /// </summary>
+    /// <returns>The reject port, or 0 when the delta pool is unavailable.</returns>
+    ValueTask<int> GetRateLimitRejectPortAsync();
 }

src/Empostor.Server/Net/Manager/ClientManager.cs

@@ -6,10 +6,12 @@ using System.Threading;
 using System.Threading.Tasks;
 using Empostor.Api.Config;
 using Empostor.Api.Events.Managers;
+using Empostor.Api.Languages;
 using Empostor.Api.Net;
 using Empostor.Api.Net.Manager;
 using Empostor.Api.Service;
 using Empostor.Server.Events.Client;
+using Empostor.Server.Http;
 using Empostor.Server.Net.Factories;
 using Empostor.Server.Service;
 using Empostor.Server.Service.Shared;
@@ -35,6 +37,8 @@ namespace Empostor.Server.Net.Manager
         private readonly PortPoolService _portPool;
         private readonly IpGeolocationService _ipGeo;
         private readonly ClientIdStore _clientIdStore;
+        private readonly IpRateLimitService _rateLimit;
+        private readonly LanguageService _language;
         private int _idLast;
 
         public ClientManager(
@@ -47,7 +51,9 @@ namespace Empostor.Server.Net.Manager
             PlayerConnectStore playerConnectStore,
             PortPoolService portPool,
             IpGeolocationService ipGeo,
-            ClientIdStore clientIdStore)
+            ClientIdStore clientIdStore,
+            IpRateLimitService rateLimit,
+            LanguageService language)
         {
             _logger = logger;
             _eventManager = eventManager;
@@ -60,6 +66,8 @@ namespace Empostor.Server.Net.Manager
             _portPool = portPool;
             _ipGeo = ipGeo;
             _clientIdStore = clientIdStore;
+            _rateLimit = rateLimit;
+            _language = language;
             _idLast = checked((int)_clientIdStore.GetLastId());
 
             if (_compatibilityConfig.AllowFutureGameVersions)
@@ -163,7 +171,15 @@ namespace Empostor.Server.Net.Manager
                 {
                     // Dynamic delta mode: an active port that has no auth info
                     // bound to it is an unauthenticated UDP connection — reject
-                    // it instead of admitting an anonymous client.
+                    // it instead of admitting an anonymous client. An IP that is
+                    // over the request quota gets the localized hint, everyone
+                    // else the plain authentication notice.
+                    if (IsRateLimited(null, clientIp, out var retryNoAuth))
+                    {
+                        await RejectRateLimitedAsync(connection, 0, language, retryNoAuth, NormalizeIp(clientIp));
+                        return;
+                    }
+
                     _logger.LogWarning(
                         "#{Id} {Name} │ port {Port} has no auth info │ {Ip} │ rejecting unauthenticated UDP connection",
                         id, name, deltaPort, NormalizeIp(clientIp));
@@ -172,6 +188,13 @@ namespace Empostor.Server.Net.Manager
                 }
 
                 // Port matched — cancel the allocation timeout
+                var limited = IsRateLimited(authInfo.ClientIp, clientIp, out var retryAfter);
+                if (limited)
+                {
+                    await RejectRateLimitedAsync(connection, deltaPort, language, retryAfter, NormalizeIp(clientIp));
+                    return;
+                }
+
                 _portPool.ConfirmPort(deltaPort);
                 // Mark the auth-cache entry as active so the inactivity
                 // timer never clears the port while the player is connected.
@@ -186,6 +209,12 @@ namespace Empostor.Server.Net.Manager
             else
             {
                 // Fixed-port mode: no auth binding, no PUID/FriendCode.
+                if (IsRateLimited(null, clientIp, out var retryAfter))
+                {
+                    await RejectRateLimitedAsync(connection, 0, language, retryAfter, NormalizeIp(clientIp));
+                    return;
+                }
+
                 _logger.LogInformation(
                     "#{Id} {Name} │ fixed port │ {Location} │ {Lang} │ {Platform}{Reactor}",
                     id, name, locationStr, lang, platformStr, reactorStr);
@@ -223,6 +252,58 @@ namespace Empostor.Server.Net.Manager
                && _clients.TryGetValue(client.Id, out var c)
                && ReferenceEquals(client, c);
 
+        // True when the IP already used up its TCP (HTTP) request quota. The
+        // IP of the HTTP handshake is preferred: behind a CDN that is the real
+        // player IP, while the UDP source address may be a proxy node.
+        private bool IsRateLimited(string? httpIp, IPAddress? udpIp, out TimeSpan retryAfter)
+        {
+            retryAfter = TimeSpan.Zero;
+
+            IPAddress? ip = null;
+            if (!string.IsNullOrEmpty(httpIp) && IPAddress.TryParse(httpIp, out var parsed))
+            {
+                ip = parsed;
+            }
+
+            ip ??= udpIp;
+            if (ip == null)
+            {
+                return false;
+            }
+
+            return _rateLimit.IsLimited(ip, out retryAfter);
+        }
+
+        // Over-quota players get a localized dialog instead of a black screen:
+        // the HTTP layer deliberately lets the join request through so the
+        // client reaches this point and can display the message.
+        private async ValueTask RejectRateLimitedAsync(
+            IHazelConnection connection,
+            int deltaPort,
+            Language language,
+            TimeSpan retryAfter,
+            string ip)
+        {
+            var minutes = IpRateLimitService.MinutesUntilRetry(retryAfter);
+            var message = _language
+                .Get(IpRateLimitService.MessageKey, language)
+                .Format(minutes)
+                .Get();
+
+            _logger.LogWarning(
+                "IpRateLimit rejecting game connection from {Ip} │ retry in {Minutes}m",
+                ip, minutes);
+
+            await connection.CustomDisconnectAsync(DisconnectReason.Custom, message);
+
+            if (deltaPort > 0)
+            {
+                // The port was never confirmed, release it right away instead
+                // of waiting for the 5-minute allocation timeout.
+                _portPool.ReturnPort(deltaPort);
+            }
+        }
+
         private static string NormalizeIp(IPAddress? addr)
         {
             if (addr == null)

src/Empostor.Server/Net/Matchmaker.cs

@@ -2,10 +2,13 @@ using System;
 using System.Collections.Concurrent;
 using System.Net;
 using System.Net.Sockets;
+using System.Threading;
 using System.Threading.Tasks;
 using Empostor.Api.Config;
 using Empostor.Api.Events.Managers;
+using Empostor.Api.Languages;
 using Empostor.Server.Events.Client;
+using Empostor.Server.Http;
 using Empostor.Server.Net.Hazel;
 using Empostor.Server.Net.Manager;
 using Empostor.Server.Service.Auth;
@@ -30,10 +33,16 @@ namespace Empostor.Server.Net
         private readonly ServerConfig _serverConfig;
         private readonly AuthCacheService _authCache;
         private readonly IOptions<AntiCheatConfig> _antiCheatOptions;
+        private readonly IpRateLimitService _rateLimit;
+        private readonly LanguageService _language;
 
         private UdpConnectionListener? _mainListener;
         private readonly ConcurrentDictionary<int, UdpConnectionListener> _deltaListeners = new();
 
+        // Shared port for over-quota (rate limited) joins; 0 until first use.
+        private int _rejectPort;
+        private readonly SemaphoreSlim _rejectPortLock = new(1, 1);
+
         private IPEndPoint? _mainEndPoint;
 
         public Matchmaker(
@@ -46,7 +55,9 @@ namespace Empostor.Server.Net
             IFirewallService firewall,
             IOptions<ServerConfig> serverConfig,
             AuthCacheService authCache,
-            IOptions<AntiCheatConfig> antiCheatOptions)
+            IOptions<AntiCheatConfig> antiCheatOptions,
+            IpRateLimitService rateLimit,
+            LanguageService language)
         {
             _eventManager = eventManager;
             _clientManager = clientManager;
@@ -58,6 +69,8 @@ namespace Empostor.Server.Net
             _serverConfig = serverConfig.Value;
             _authCache = authCache;
             _antiCheatOptions = antiCheatOptions;
+            _rateLimit = rateLimit;
+            _language = language;
 
             // Subscribe to port return events from the pool
             _portPool.OnPortReturned += OnPortReturned;
@@ -189,6 +202,66 @@ namespace Empostor.Server.Net
             }
         }
 
+        /// <summary>
+        ///     One shared UDP port for all over-quota joins: reserving it here
+        ///     (once) means rate-limited TCP requests never take a pool port and
+        ///     never start their own listener. The listener above answers every
+        ///     handshake on this port with the localized hint and closes it, so
+        ///     the player is told why they cannot join instead of seeing a black
+        ///     screen — without letting them into a game.
+        /// </summary>
+        public async ValueTask<int> GetRateLimitRejectPortAsync()
+        {
+            if (!_portPool.IsEnabled)
+            {
+                // Fixed-port mode: the main listener is the reject target.
+                return 0;
+            }
+
+            var existing = Volatile.Read(ref _rejectPort);
+            if (existing > 0)
+            {
+                return existing;
+            }
+
+            await _rejectPortLock.WaitAsync();
+            try
+            {
+                existing = Volatile.Read(ref _rejectPort);
+                if (existing > 0)
+                {
+                    return existing;
+                }
+
+                var port = _portPool.AllocatePort("(rate limit reject)");
+                if (port <= 0)
+                {
+                    _logger.LogWarning("Matchmaker could not reserve the rate-limit reject port: pool unavailable");
+                    return 0;
+                }
+
+                if (!await StartDeltaListenerAsync(port))
+                {
+                    // StartDeltaListenerAsync already returned the port.
+                    return 0;
+                }
+
+                // Confirmed so it is never reclaimed by the allocation timeout:
+                // this port lives for the whole lifetime of the server.
+                _portPool.ConfirmPort(port);
+                Volatile.Write(ref _rejectPort, port);
+
+                _logger.LogInformation(
+                    "Matchmaker rate-limit reject port reserved on {Port} (one shared port for all over-quota joins)",
+                    port);
+                return port;
+            }
+            finally
+            {
+                _rejectPortLock.Release();
+            }
+        }
+
         public async ValueTask StopAsync()
         {
             if (_mainListener != null)
@@ -228,6 +301,21 @@ namespace Empostor.Server.Net
                     out var platformSpecificData);
 
                 connection = new HazelConnection(e.Connection, _connectionLogger, _antiCheatOptions);
+
+                // Shared rate-limit reject port: there is no auth entry and no
+                // player behind it, so the only thing to do is tell the client
+                // — in its own language — why it is not let in.
+                if (port != 0 && port == Volatile.Read(ref _rejectPort))
+                {
+                    var message = BuildRateLimitMessage(connection.EndPoint?.Address, language);
+                    _logger.LogWarning(
+                        "Matchmaker rate limit rejected {Ip} on reject port {Port} │ {Message}",
+                        connection.EndPoint?.Address?.ToString() ?? "unknown", port, message);
+
+                    await connection.CustomDisconnectAsync(DisconnectReason.Custom, message);
+                    return;
+                }
+
                 await _eventManager.CallAsync(new ClientConnectionEvent(connection, e.HandshakeData));
                 await _clientManager.RegisterConnectionAsync(
                     connection, name, clientVersion, language, chatMode, platformSpecificData,
@@ -244,6 +332,22 @@ namespace Empostor.Server.Net
             }
         }
 
+        // Localized "please try again in N minutes" hint. N is what is actually
+        // left for that IP when it can be read off the quota, the full window
+        // otherwise (behind a CDN the UDP source address may not be the key the
+        // requests were counted with).
+        private string BuildRateLimitMessage(IPAddress? ip, Language language)
+        {
+            var minutes = Math.Max(1, _antiCheatOptions.Value.IpRateLimitWindowMinutes);
+
+            if (ip != null && _rateLimit.IsLimited(ip, out var retryAfter))
+            {
+                minutes = IpRateLimitService.MinutesUntilRetry(retryAfter);
+            }
+
+            return _language.Get(IpRateLimitService.MessageKey, language).Format(minutes).Get();
+        }
+
         private void OnPortReturned(int port)
         {
             _authCache.RemoveByPort(port);

src/Empostor.Server/Program.cs

@@ -173,6 +173,7 @@ namespace Empostor.Server
                     services.AddSingleton<GameManager>();
                     services.AddSingleton<IGameManager>(p => p.GetRequiredService<GameManager>());
                     services.AddSingleton<ListingManager>();
+                    services.AddSingleton<IpRateLimitService>();
 
                     services.AddEventPools();
 
@@ -263,6 +264,10 @@ namespace Empostor.Server
                     });
                     builder.Configure(app =>
                     {
+                        // Anticheat IP request rate limit — runs before every
+                        // HTTP (TCP) endpoint, including the plugin ones.
+                        app.UseMiddleware<IpRateLimitMiddleware>();
+
                         foreach (var p in app.ApplicationServices.GetRequiredService<PluginLoaderService>().Plugins)
                             if (p.Startup is IPluginHttpStartup s)
                             {

src/Empostor.Server/config.json

@@ -29,7 +29,10 @@
     "EnableTargetChecks": true,
     "ForbidProtocolExtensions": true,
     "EnablePacketSizeChecks": true,
-    "PacketSizeLimit": 1203
+    "PacketSizeLimit": 1203,
+    "EnableIpRateLimit": true,
+    "IpRateLimitRequests": 30,
+    "IpRateLimitWindowMinutes": 5
   },
   "Timeout": {
     "SpawnTimeout": 5000,