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.

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.

Configuration

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

[ModSync]

[Security]

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.

Compatibility

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