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Fuzz testing is a software testing technique used to find security and stability issues by providing pseudo-random data as input to the software.AFLplusplus is a popular, effective, and modern fuzz testing tool based onAFL. This library, afl.rs, allows one to run AFLplusplus on code written inthe Rust programming language.

Documentation can be found in theRust Fuzz Book.

Screen recording of AFL running on Rust code.

Before starting to fuzz, you should reconfigure your system for optimalperformance and better crash detection. This can be done withcargo afl system-config.But this subcommand requires root, so it uses sudo internally. Hence, you might need to enteryour password.

By default, the AFL++CMPLOGfeature is activated, which helps to achieve good code coverage.However, it is not beneficial to activate CMPLOG on more than two instances.So if you run multiple AFL++ instances on your fuzzing target, you can disable CMPLOG by specifying the command line parameter '-c -'.

Thisdocumentwill familiarize you with AFL++ features to help in running a successful fuzzing campaign.

By default, thefuzzing config is set whencargo-afl is used to build. If you want to prevent this, just set theenvironment variableAFL_NO_CFG_FUZZING to1 when building.