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188 Stars 50 Forks GNU General Public License v3.0 358 Commits 4 Opened issues


An automated KoiVM disassembler and devirtualisation utility

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Project Old Rod - KoiVM Devirtualisation tool

License: GPL v3 Master branch build status

Project Old Rod is an automated command-line utility that attempts to disassemble any .NET application protected by the KoiVM virtualiser plugin for ConfuserEx. Additionally, it tries to recompile the VM code back to .NET CIL in an attempt to recover the original code.

Project Old Rod is released under the GPLv3 license.


  • N00b users: Just drag and drop the protected executable in

    and observe how the majestic Magikarp fixes your code all by itself. Pretty nice huh?
  • Advanced users: Old Rod has a lot of features! Type the following command in a terminal to get an overview of all available options and flags:

    OldRod.exe --help

    Some of the niceties include:

    • --output-directory
      , which sets the output directory (who would have thought!?).
    • --koi-stream-name
      , which help the magestic Magikarp finding the data it needs.
    • --config
      for providing a custom constants mapping, see example-config.json for an example configuration file.
    • --no-pause
      if you don't like pressing a key to continue at the end of it all.


The devirtualiser is powered by the following projects: - AsmResolver: .NET inspection library License: MIT - Rivers: Graph analysis library License: MIT - Newtonsoft.JSON: JSON file parser. License: MIT

These are submodules or nuget packages. Be sure to clone/restore all of them when building the project.


Get the latest build from the AppVeyor build server.

Alternatively, you can build the project yourself using MSBuild or an IDE that works with MSBuild (such as Visual Studio and JetBrains Rider).


Is Old Rod a deobfuscator?

No. It only disassembles the code and recompiles it. It will not simplify control flow, nor will it decrypt your strings, simplify arithmetic expressions, rename all symbols, decrypt resources, or anything like that. For this, other tools exist.

Will Old Rod support modifications of KoiVM?

Yes and no.

Old Rod's recompiler is quite generic and is built to be able to resist several architectural changes. For example, it does not rely on hardcoded opcode sequences or the like in the actual virtualized code. See here for more information on how that is done. Furthermore, there are some command-line arguments that you can use to override certain auto detection systems and behaviour (see

OldRod.exe --help

That being said, it will always be possible to break Old Rod's automatic detection systems with very minimal changes to vanilla KoiVM (lazy modifications such as changing the signature of the methods in

). It is not worth the time and effort to support each and every one of them that can be found on the internet, unless one of these mods gets very popular. Therefore, don't expect drag-n-drop to always work on binaries protected by modifications of KoiVM, nor support for them in the near future.

Heeeeeelp! it...

  • ... crashes,
  • ... prints errors I don't want to read,
  • ... produces corrupted files.

These are features, not bugs. You can turn them off by using:

OldRod.exe  --dont-crash --no-errors --no-output-corruption

If the above does not work, please consider going to the issue tracker and file a detailed bug report, preferably using the issue template and sample binary.

How do I troubleshoot Old Rod?

Old Rod has quite a few diagnostics built-in that might help you out: -

) or
) will print debug and full error messages to the standard output. -
will produce a
in the output directory containing a log that is similar to enabling
. You don't need to include
to get a verbose output in the log file. -
will create all kinds of dumps of intermediate steps of the devirtualisation process in the output directory. -
will rename most (but not all) symbols in the KoiVM runtime library to something more meaningful. -
--only-export 1,2,3
--ignore-export 1,2,3
will only include or exclude exports 1, 2 and 3 respectively. -
will let the devirtualiser try to recover from errors as much as possible. Note that this is a very mysterious feature, and enabling this feature might have cool side-effects and result in incorrect binaries being produced.

Why did you create this?

I thought it would be a cool project.

Why did you release this?

The original author of KoiVM released the source code for free.

Why is the project so complicated?

Because KoiVM is more complicated than the average VM that is out there for .NET. Check out the docs to find out how the recompiler works.

Also I am probably not the best coder or reverse engineer.

Couldn't you just use pattern matching for every CIL instruction like normal people?

Sure, but I am stubborn, I don't like to write countless of patterns, and I like writing compilers. The last reason is also the main reason this project was started in the first place.

What is the OldRod.Core.CodeGen namespace that is injected?

Not all instructions are always perfectly translated to CIL, and still require some of the original features of KoiVM (most notably, the flags register as the CLR does not have one). For this, the code generator might inject some code to emulate the behaviour of these features. This is put into this namespace.

What's with the name and the Magikarp?

In the original release of KoiVM, the plugin description mentions a Magikarp virtualising your code. In the original Pokémon games, the best way to catch a Magikarp is using an old rod.


Honestly, I don't know, I am probably weird...

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