Invalid Metadata

Protection ID: invalid_metadata

This protection adds invalid metadata to the modules to prevent the decompiler from rebuilding them.

This protection is available in the editions:

Team Scale Enterprise

How It Works

Invalid metadata protection modifies the .NET assembly metadata in ways that confuse and break decompilers while still allowing the CLR (Common Language Runtime) to execute the code correctly. This protection injects specially crafted metadata structures that are technically valid for runtime execution but cause decompilers to generate errors or invalid code.

The CLR is more forgiving of certain metadata anomalies than decompilers, which typically expect well-formed, standard metadata structures. This protection exploits that difference to create assemblies that run normally but resist decompilation.

Parameters

This protection has no parameters or settings.

Rules configuration

• shield.config.json

{
  "protections": {
    "invalid_metadata": {}
  }
}

Modes

• Default: Add invalid metadata to prevent the code from being decompiled.

Code Example

This protection works at the assembly metadata level and doesn't require or show changes in your source code. Its effects are most noticeable when someone attempts to decompile your protected assembly and encounters errors like:

Error: Could not resolve type with token 01000321 from typeref (expected class 'System.Object' in assembly 'mscorlib, Version=4.0.0.0')
Error: Failed to resolve assembly 'AssemblyRef:0x2' at token 0x23000002
Unable to load metadata for module 'YourAssembly.dll'

Exclusions

• Exclude with attribute

Include this attribute in your source code:

[Obfuscation(Exclude = false, Feature = "-invalid_metadata")]

• Exclude from the interface

You can exclude this protection from methods or classes you want using the Shield configuration interface.

When to Use

Invalid metadata protection is most effective when:

• Standalone applications: Applications that are not loaded via reflection by other applications
• Final application builds: End-user applications where the assembly is directly executed
• Desktop applications: Windows applications where the assembly is loaded directly by the OS
• Anti-decompilation strategy: As part of a comprehensive strategy to prevent reverse engineering

Use caution or avoid invalid metadata protection when:

• Plugin systems: Assemblies loaded dynamically as plugins for other applications
• Libraries referenced by reflection: If your code is loaded via reflection by another application
• AOT compilation: Applications using Ahead-of-Time compilation may have issues
• Mobile platforms: Some mobile frameworks perform stricter metadata validation

Compatibility

Shield is compatible with all versions of .NET. It automatically adapts to your specific framework, whether you're using .NET 2.0, .NET 4.7, .NET Core 2.1, or Xamarin.Forms 5.0.