Darknet – The Darkside

FuzzDiff is a simple tool to help make crash analysis during file format fuzzing a bit easier. I’m sure many people have written similar tools for their own purposes, but I haven’t seen any that are publicly available. Hopefully at least one person finds it useful.

When provided with a fuzzed file, a corresponding original un-fuzzed file, and the path to the targeted program, FuzzDiff will selectively “un-fuzz” portions of the fuzzed file while re-launching the application to monitor for crashes. This will yield a file that still crashes the target application, but contains a minimum set of changes from the original, un-fuzzed file. This can be useful in pinning down the exact cause of a crash.

The tool is written in Python and currently only works on Unix-based systems, since it monitors for crashes by checking for SIGSEGV. It also assumes that the target program adheres to the syntax “[program] [args] [input file]“. Both of these limitations can be easily worked around. The code is hardly what I’d call production-ready, but it gets the job done.

You can download FuzzDiff here:

fuzzdiff.py

Or read more here.