This is experimental module that enables American Fuzzy Lop fork server and instrumentation for pure-Python code.
Add this code (ideally, after all other modules are already imported) to the target program:
import afl afl.init()
The instrumentation is currently implemented with a trace function, which is called whenever a new local scope is entered. You might need to wrap the code of the main program in a function to get it instrumented correctly.
Optionally, add this code at the end of the target program:
This should speed up fuzzing considerably, at the risk of not catching bugs that could happen during normal exit.
For persistent mode, wrap the tested code in this loop:
while afl.loop(N): ...
Nis the number of inputs to process before restarting.
You shouldn't call
afl.init()in this case.
If you read input from
sys.stdin, you must rewind it in every loop iteration:
afl-fuzz ≥ 1.82b is required for this feature.
Use py-afl-fuzz instead of afl-fuzz:
$ py-afl-fuzz [options] -- /path/to/fuzzed/python/script [...]
The instrumentation is a bit slow at the moment, so you might want to enable the dumb mode (
-n), while still leveraging the fork server.
afl-fuzz ≥ 1.95b is required for this feature.
The following environment variables affect python-afl behavior:
If this variable is set, python-afl installs an exception hook that kills the current process with the selected signal. That way afl-fuzz can treat unhandled exceptions as crashes.
By default, py-afl-fuzz, py-afl-showmap, python-afl-cmin, and py-afl-tmin set this variable to
You can set
PYTHON_AFL_SIGNALto another signal; or set it to
0to disable the exception hook.
Persistent mode is enabled only if this variable is set.
py-afl-fuzz sets this variable automatically, so there should normally no need to set it manually.
- TSTL test harness code is ignored if this variable is set; relevant only to users of TSTL interface to python-afl.
- Taking a look at python-afl by Jussi Judin
- Introduction to Fuzzing in Python with AFL by Alex Gaynor
- AFL's README
To build the module, you will need:
- Python 2.6+ or 3.2+
- Cython ≥ 0.19 (only at build time)
py-afl-fuzz requires AFL proper to be installed.