AFL++

AFL++ is a fuzzing framework derived from American Fuzzy Lop (AFL) by Michał Zalewski. It was created to bring together the improvements developed over the years for fuzzers of the AFL family that were never merged into AFL, which has not been updated since November 2017.

The framework includes afl-fuzz, a fuzzer with many mutators and configurations; source code instrumentation modules (LLVM mode, afl-as and a GCC plugin); binary instrumentation modules (QEMU, Unicorn and QBDI modes); and utilities for minimising test cases and corpora. It is used to find crashes and security vulnerabilities by feeding programs with mutated inputs.

AFL++ is open source and actively developed on GitHub; version 5.03c was released in September 2026.