Nimfilt is a collection of modules and scripts to help with analyzing Nim binaries. It started out as a CLI demangling tool inspired by c++filt.

It evolved into a larger set of tools for analyzing Nim, but the original name stuck.

  • nimfilt.py: a Python module that implements demangling for Nim. It can also be run as basic CLI tool.
  • id_nim_binary.yar: a set of YARA rules to identify Nim ELF and PE binaries.
  • nimimfilt_ida.py: Nimfilt for IDA, an IDApython script to help reverse-engineers handle Nim binaries.

Context

Nim is compiled to another language (usually C/C++) before being compiled to a native executable. It also doesn’t include a large runtime.

However, the process still leaves some Nim-specific artefacts and specificites in in the produced binary.

For one, method and module names are mangled using, Nim’s own name scheme which is distinct from C++’s.

This scheme isn’t documented so I relied on the source code of the Nim compiler.

Most of this name mangling in implemented in compiler/msgs.nim and compiler/ccgtypes.nim.

Nimfilt For IDA

The IDAPython script can be run as a one-off or installed as a plugin.

If running as a script, simply launch it from the Nimfilt project directory. It is recommended to do so after auto-analysis has completed and you’ve loaded any additional FLIRT signatures.

Plugin Setup Using Sark‘s Plugin Loader

Add <nimfilt_project_dir>/nimfilt_ida.py to your your plugins.list as per their instruction on installing plugins.

Manual Plugin Setup

  1. Copy nimfilt.py to a directory that is included in your IDAPython’s PYTHONPATH (commonly <IDA_install_dir>/python/ or %APPDATA%/Hex-Rays/IDA Pro/python/3/).
  2. Copy nimfilt_ida.py to your IDAPython plugin directory (usually <IDA_install_dir>/plugins/)

Usage

*Note: The current version of Nimfilt for IDA only supports one command which runs all analyses. *

Navigate to Edit -> Plugins -> Nimfilt and click on it.

You can set Nimfilt to automatically execute when a loaded file is recognized as a Nim binary. To do so, set the AUTO_RUN global variable to True in nimfilt_ida.py

Features

Current features include:

  • Identifying if a loaded file is a Nim binary.
  • Demangling Nim function and package names.
  • Demangling Nim package init function names.
  • Organizing functions into directories by package.
  • Identifying, typing and renaming Nim strings.

Published by Tamil S

Tamil has a great interest in the fields of Cyber Security, OSINT, and CTF projects. Currently, he is deeply involved in researching and publishing various security tools with Kali Linux Tutorials, which is quite fascinating.

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