s&box Sandbox Security Model: Assembly Whitelist, Blocked APIs, Reflection Restrictions, and Safe Assembly Caching

s&box Sandbox Security Model: Assembly Access Control and Whitelisted APIs

s&box uses a whitelist-based security model to prevent game code from accessing dangerous APIs. All game assemblies are verified against AccessRules before being loaded.

How It Works

The AccessControl system uses Mono.Cecil to inspect compiled assemblies at the IL level. Every method call, field access, and type reference is checked against a whitelist of allowed patterns. If any disallowed access is found, the assembly is rejected.

Whitelisted Assemblies

Game code can reference these assemblies:

• Sandbox.Engine, Sandbox.System, Sandbox.Filesystem, Sandbox.Reflection, Sandbox.Mounting


• System.Private.CoreLib (with restrictions)


• System.Text.Json, System.Linq, System.Collections, System.Collections.Concurrent


• System.Text.RegularExpressions, System.IO.Compression


• System.Security.Cryptography (MD5, SHA1, SHA256, SHA512 only)


• System.Net.Http (HttpResponseMessage, HttpContent, etc.)


• System.Threading.Channels, System.Memory

What's Blocked

Notable restrictions in System.Private.CoreLib:

• System.IO.Path.Exists, GetFullPath, GetTempFileName, GetTempPath — blocked


• System.Buffers.ArrayPool.Shared — blocked (use PublicArrayPool instead)


• System.Reflection — only basic read-only access (no Invoke, no GetValue/SetValue)


• System.Delegate constructors and CreateDelegate — blocked


• System.GC — only SuppressFinalize allowed


• System.Environment — only CurrentManagedThreadId and StackTrace

Reflection Restrictions

Game code can read reflection metadata (names, types, attributes) but cannot invoke methods or get/set property values via reflection. Use Game.TypeLibrary instead for safe reflection.

SHA256 Hashing

// This is allowed in game code
using var sha256 = System.Security.Cryptography.SHA256.Create();
var hash = sha256.ComputeHash( data );

HTTP Requests

// HttpClient is NOT directly accessible — use Sandbox.Http or Game.Http instead
// But HttpResponseMessage, HttpContent etc. are accessible for handling responses

Safe Assembly Caching

Once an assembly passes verification, its SHA256 hash is cached. If the same assembly bytes are seen again, the cached result is used without re-verifying.