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zzuf - multi-purpose fuzzer

zzuf is a transparent application input fuzzer. Its purpose is to find bugs in applications by corrupting their user-contributed data (which more than often comes from untrusted sources on the Internet). It works by intercepting file and network operations and changing random bits in the program’s input. zzuf’s behaviour is deterministic, making it easier to reproduce bugs. Its main areas of use are:

  • quality assurance: use zzuf to test existing software, or integrate it into your own software’s testsuite
  • security: very often, segmentation faults or memory corruption issues mean a potential security hole, zzuf helps exposing some of them

zzuf’s primary target is media players, image viewers and web browsers, because the data they process is inherently insecure, but it was also successfully used to find bugs in system utilities such as objdump.

zzuf is not rocket science. The idea of fuzzing input data is barely new. zzuf’s only purpose is to make things easier and automated.

I gave a few talks about zzuf. The slides contain information you may find useful:

See also an impressive list of bugs found with zzuf.


Download zzuf (source code) from zzuf-0.12.tar.gz (13 June 2008). Supported platforms are: Linux (glibc), FreeBSD, OpenBSD, Mac OS X. There is no Windows port yet and NetBSD is almost working.

zzuf tutorial

The zzuf tutorial is a hands-on guide to the most important zzuf features. It starts with the working principles but goes on with very advanced uses of the tool.

Warning: this tutorial requires zzuf version 0.11 or later.

  1. Basic zzuf usage
    1.1. Launching zzuf
    1.2. Invoking different programs
    1.3. The fuzzing ratio
    1.4. The random seed
    1.5. Creating fuzzed files
  2. zzuf as a batch testing tool
    2.1. Debug mode
    2.2. Include and exclude patterns
    2.3. Seed ranges
    2.4. Ratio ranges


Development happens in a centralised Subversion repository:

There is also a Git repository that mirrors the central one:

If you want to discuss zzuf or report bugs, you can write to me at or join #libcaca on

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