GyattAntiCheat

A lightweight, high-performance client-server anti-cheat and mod synchronization framework for Valheim.

Designed with an asynchronous multi-threaded architecture, GyattAntiCheat operates completely off the main Unity thread to prevent frame drops, micro-stutters, and freezes while actively monitoring for external trainers, memory modifications, and unauthorized mods.

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Key Features

1. Zero-Stutter Trainer & Process Detection

• Win32 Desktop Scanner: Uses native EnumWindows and process queries to detect third-party cheats (e.g., FLiNG Trainer, WeMod, Cheat Engine) even when running with elevated Administrator (UAC) permissions.
• Asynchronous Execution: Runs on a dedicated background CPU thread every 30 seconds.
• Smart Filtering: Built-in exclusions for common web browsers (Chrome, Edge, Firefox, Brave, Opera) to prevent false positives when searching or chatting online.

2. In-Game State & Memory Hack Prevention

Monitors player memory every 3 seconds for values that deviate from vanilla mechanics:

• God Mode & Health Locks: Detects InGodMode, abnormal max health (> 450 HP), and locked/frozen HP.
• Infinite Stamina: Detects abnormal stamina (> 380) and frozen stamina values.
• Eitr (Magic) Hacks: Detects Eitr generation without consuming Eitr foods, abnormal Eitr (> 350), and frozen Eitr values.
• Carry Weight Hack: Detects modified carry capacity (e.g., FLiNG's 999,999 kg). Calibrated with a safe threshold (> 1,200 kg) to fully accommodate all legitimate in-game buffs combined (Base + Megingjord + Troll Mead + Fader Power + Corpse Run).
• Infinite Item Durability: Flags weapons, armor, and tools whose durability exceeds legitimate maximum caps.
• Infinite Food & Rested Duration: Detects frozen status effect timers while respecting legitimate 50-minute Bog Witch Feasts and high-comfort Rested buffs.
• Fast Skill Level Up: Catches rapid consecutive skill level-ups (the trainer 1-hit-per-level pattern) and skills exceeding level 100.
• Free Crafting & Building: Catches unauthorized m_noPlacementCost (building without materials).
• Fly & Ghost Mode: Detects IsDebugFlying, m_flying (ZFly), and InGhostMode.

3. Server Mod Synchronization (ModSync)

• Instant Connection Handshake: Exchanges and validates mod lists during RPC_PeerInfo (first second of connection), completely eliminating timeout kicks on players with slower PCs loading heavy worlds.
• Physical DLL Auto-Whitelist: Scans physical .dll files in the server's BepInEx/plugins/ folder to ensure headless client-side mods (such as UI mods) are correctly recognized and allowed.
• Unauthorized & Missing Mod Enforcement: Blocks clients running unapproved extra mods and requires mandatory server mods.
• Client Enforcement: Automatically kicks players connecting with a vanilla client or missing GyattAntiCheat.dll.

4. Anti-Dupe Delayed Kick

• When a cheater is flagged, the client is immediately instructed to perform an emergency profile save (Game.instance.SavePlayerProfile).
• The server delays the network disconnection by 2 seconds, giving server-character sync mods (like Reef Characters or ServerCharacters) enough time to write the latest .fch file to disk.
• Prevents container rollbacks and item duplication exploits upon reconnecting.

5. Full Admin Exemption & Live Alerts

• Players listed in adminlist.txt automatically bypass all restrictions, state scans, and mod whitelist checks.
• When a violation is triggered by a player, all connected Admins receive real-time alert notifications directly on their HUD and in-game chat with player names and IDs.

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Configuration

The configuration file is generated at BepInEx/config/com.valheim.gyattanticheat.cfg after the first run:

[ModSync]

Setting	Default	Description
EnforceServerModWhitelist	true	Prevents players from joining with mods that are not installed on the server.
CheckMissingServerMods	true	Requires players to have all mods installed on the server (excluding ServerOnlyMods).
AllowedClientOnlyMods	org.bepinex.plugins.configurationmanager,...	Comma-separated list of mod GUIDs or names permitted on clients even if not present on the server (e.g., UI or graphic enhancements).
ServerOnlyMods	discordconnector,server_devcommands	Comma-separated list of mod GUIDs or names installed exclusively on the server that clients are not required to download.

[Security]

Setting	Default	Description
BlacklistedKeywords	wemod,cheatengine,trainer,fling,...	Comma-separated list of restricted process names, window titles, or mod keywords.
AutoKickCheater	true	Automatically kicks non-admin players when a violation or mod mismatch is detected (Server only).
RequireGyattAntiCheat	true	Kicks players who attempt to connect without the mod installed (Server only).

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Installation

For Dedicated Servers:

1. Ensure BepInExPack Valheim is installed.
2. Place GyattAntiCheat.dll into your server's BepInEx/plugins/ directory.
3. Configure adminlist.txt in the server save folder to grant Admin bypass.

For Clients (Players):

1. Install BepInExPack Valheim (via Thunderstore / r2modman or manual install).
2. Place GyattAntiCheat.dll into your Valheim/BepInEx/plugins/ directory.

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Compatibility

• Fully compatible with Valheim (Ashlands & The Bog Witch update).
• Compatible with Reef Characters, ServerCharacters, and Jotunn.
• Crossplay & Steam dedicated server compatible.