re-dotnet

MCP server for .NET assembly analysis. Vendor-neutral wrapper around AsmResolver (PE + .NET metadata) and ICSharpCode.Decompiler / ILSpy (C# decompiler).

Why

The other RE-AI MCP servers (re-lief, re-rizin, re-capa) handle native PE, ELF, MachO, DEX, ART, OAT — but none of them read the .NET CLI header or the ECMA-335 metadata tables. A MonoLauncher-style launcher that ships its payload as a managed .NET assembly is invisible to those tools; the import hash is empty, the strings table is uninformative, and rizin only sees native wrapper code.

re-dotnet fills that gap. It enumerates TypeDef / MethodDef / FieldDef, walks the #US string heap, and decompiles a single class or method to C# on demand.

Architecture

The MCP server itself is pure Python. The heavy lifting is done by a small .NET 10 CLI binary, re-dotnet-cli, built from src/re_dotnet/dotnet/Re.Dotnet.Cli/:

Claude Code (MCP stdio)
  │
  ▼
re-dotnet server (Python, this directory)
  │  subprocess.run(...)
  ▼
re-dotnet-cli (self-contained .NET 10 binary, single-file publish)
  │
  ├─ AsmResolver 6.x        (PE + .NET metadata, obfuscation-robust)
  └─ ICSharpCode.Decompiler 9.x  (C# decompiler)

The subprocess boundary is intentional:

• No pythonnet. pythonnet is a fragile ABI bridge that breaks on every Python minor. Process isolation is robust.
• No Mono. .NET 10 is the only supported runtime.
• Single-file publish. The CLI is a self-contained binary; no dotnet --info dance, no DOTNET_ROOT env vars, no GAC.

The Python wrapper locates the binary via this fallback chain (see runner.py):

1. $RE_DOTNET_CLI_PATH (escape hatch for tests)
2. <server>/bin/re-dotnet-cli (install.sh default)
3. The dev build under src/re_dotnet/dotnet/.../bin/
4. re-dotnet-cli on $PATH

Tools

Tool	What it does
check_dotnet	Health check — return .NET runtime + AsmResolver + Decompiler versions
parse_assembly	Enumerate TypeDef rows; return assembly header + one row per type
decompile_type	Decompile a single class to C# via ILSpy
decompile_method	Decompile a single method to C# via ILSpy
list_strings	Walk field-default constant strings (the #US heap subset)
get_entry_point	Return the managed entry point (<Module>::.cctor or Main)

Install

./install.sh builds the .NET CLI via dotnet publish and copies the resulting binary to servers/re-dotnet/bin/.

To build standalone:

cd servers/re-dotnet/src/re_dotnet/dotnet/Re.Dotnet.Cli
dotnet publish -c Release -o ../../../../bin

To run:

re-dotnet                          # stdio transport (default for MCP)
python -m re_dotnet                # equivalent

Requirements

• .NET 10 SDK or runtime (dotnet --version ≥ 10.0)
• 2 GB disk for the .NET SDK + the self-contained binary

Deobfuscation notes

The ILSpy decompiler produces clean C# for non-obfuscated assemblies. For binaries that have been through commercial obfuscation (control-flow flattening, string encryption, JIT-hooking), the decompiler will surface Unable to decompile ... errors. The remediation path is to run the .NET deobfuscator first (the OSS de4dot shells out, GPL-3.0 — the RE-AI plugin keeps it process-isolated so the plugin's own distribution stays clean) and then re-run decompile_type / decompile_method on the cleaned output.

Pairing with re-leak-scan

A .NET-style launcher that calls out to telemetry endpoints (Sentry, Logstash, Confluence, Google Drive) will have those URLs as field-default constants. Run re-leak-scan (T2.2) on the assembly, or call list_strings here and pipe the output through a regex filter for the four endpoint families.