Saturday, July 5, 2014

Releasing Stupid v0.1 - The Dumbest File Format Fuzzer (Python+Pydbg)

I developed Stupid in late 2011 to automate fuzzing and problem/app fault detection process of different file formats( mainly Music/Video players etc). I've been receiving many email from my readers asking me to release POC of a python + pydbg fuzzer. So today I'm very happy to make this small yet effective Fuzzer open to everyone. This is highly prototypal and I recommend to rewrite/modify the test case generator sub routine to make this fuzzer more effective.

Happy fuzzing guys. If you are lucky enough to find any zero day using this fuzzer, you can drop me a TY email or buy me a beer in return if we meet someday :)

Source Code:

Stupid source code is available @


This software is licenced under a Beerware licence although the following libraries are included with Stupid and are licensed separately.

  • pydbg
  • paimei -

Running this Fuzzer:

Stupid was developed and tested with Win32 Python 2.7(x86). So it's recommended to use the same version of python. Also make sure pydbg(x86) is installed on the system.

You need to provide the target application binary path (.exe) and at least one base file to run this fuzzer. You can to modify the configuration section of "" as per your requirement.

Test Case Generation:

mutate() routine is responsible for generating test cases from given bases files. It has two sub parts:
  • Bitflip
  • Random Byte Flip

You may want to change / modify these routines to make this fuzzer more effective. ;)


To monitor target application for different types of crashes (access violation), Stupid uses pydbg(Python debugger).It also uses "utils" of framework to collect crash information which can be used later to identify/distinguish interesting app crashes. Sample crash synopsis file is below,

Reproducing Crashes:

Crash files and crash information can be found in "Crashes" folder which can be used to reproduce app crashes.