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American Fuzzy Lop plus plus (AFL++)

Release version: 4.10c

GitHub version: 4.10c


AFL++ is maintained by:

Originally developed by Michal “lcamtuf” Zalewski.

AFL++ is a superior fork to Google's AFL - more speed, more and better mutations, more and better instrumentation, custom module support, etc.

You are free to copy, modify, and distribute AFL++ with attribution under the terms of the Apache-2.0 License. See the LICENSE for details.

Getting started

Here is some information to get you started:

  • For an overview of the AFL++ documentation and a very helpful graphical guide, please visit docs/
  • To get you started with tutorials, go to docs/
  • For releases, see the Releases tab and branches. The best branches to use are, however, stable or dev - depending on your risk appetite. Also take a look at the list of important changes in AFL++ and the list of features.
  • If you want to use AFL++ for your academic work, check the papers page on the website.
  • To cite our work, look at the Cite section.
  • For comparisons, use the fuzzbench aflplusplus setup, or use afl-clang-fast with AFL_LLVM_CMPLOG=1. You can find the aflplusplus default configuration on Google's fuzzbench.

Building and installing AFL++

To have AFL++ easily available with everything compiled, pull the image directly from the Docker Hub (available for both x86_64 and arm64):

docker pull aflplusplus/aflplusplus
docker run -ti -v /location/of/your/target:/src aflplusplus/aflplusplus

This image is automatically published when a push to the stable branch happens (see branches). If you use the command above, you will find your target source code in /src in the container.

Note: you can also pull aflplusplus/aflplusplus:dev which is the most current development state of AFL++.

To build AFL++ yourself - which we recommend - continue at docs/

Quick start: Fuzzing with AFL++

NOTE: Before you start, please read about the common sense risks of fuzzing.

This is a quick start for fuzzing targets with the source code available. To read about the process in detail, see docs/

To learn about fuzzing other targets, see:

Step-by-step quick start:

  1. Compile the program or library to be fuzzed using afl-cc. A common way to do this would be:

    CC=/path/to/afl-cc CXX=/path/to/afl-c++ ./configure --disable-shared
    make clean all
  2. Get a small but valid input file that makes sense to the program. When fuzzing verbose syntax (SQL, HTTP, etc.), create a dictionary as described in dictionaries/, too.

  3. If the program reads from stdin, run afl-fuzz like so:

    ./afl-fuzz -i seeds_dir -o output_dir -- \
    /path/to/tested/program [...program's cmdline...]

    To add a dictionary, add -x /path/to/dictionary.txt to afl-fuzz.

    If the program takes input from a file, you can put @@ in the program's command line; AFL++ will put an auto-generated file name in there for you.

  4. Investigate anything shown in red in the fuzzer UI by promptly consulting docs/

  5. You will find found crashes and hangs in the subdirectories crashes/ and hangs/ in the -o output_dir directory. You can replay the crashes by feeding them to the target, e.g. if your target is using stdin:

    cat output_dir/crashes/id:000000,* | /path/to/tested/program [...program's cmdline...]

    You can generate cores or use gdb directly to follow up the crashes.

  6. We cannot stress this enough - if you want to fuzz effectively, read the docs/ document!


Questions? Concerns? Bug reports?


The following branches exist:

  • release: the latest release
  • stable/trunk: stable state of AFL++ - it is synced from dev from time to time when we are satisfied with its stability
  • dev: development state of AFL++ - bleeding edge and you might catch a checkout which does not compile or has a bug. We only accept PRs (pull requests) for the ‘dev’ branch!
  • (any other): experimental branches to work on specific features or testing new functionality or changes.

Help wanted

We have several ideas we would like to see in AFL++ to make it even better. However, we already work on so many things that we do not have the time for all the big ideas.

This can be your way to support and contribute to AFL++ - extend it to do something cool.

For everyone who wants to contribute (and send pull requests), please read our contributing guidelines before you submit.

Special thanks

Many of the improvements to the original AFL and AFL++ wouldn't be possible without feedback, bug reports, or patches from our contributors.

Thank you! (For people sending pull requests - please add yourself to this list :-)

  Jann Horn                             Hanno Boeck
  Felix Groebert                        Jakub Wilk
  Richard W. M. Jones                   Alexander Cherepanov
  Tom Ritter                            Hovik Manucharyan
  Sebastian Roschke                     Eberhard Mattes
  Padraig Brady                         Ben Laurie
  @dronesec                             Luca Barbato
  Tobias Ospelt                         Thomas Jarosch
  Martin Carpenter                      Mudge Zatko
  Joe Zbiciak                           Ryan Govostes
  Michael Rash                          William Robinet
  Jonathan Gray                         Filipe Cabecinhas
  Nico Weber                            Jodie Cunningham
  Andrew Griffiths                      Parker Thompson
  Jonathan Neuschaefer                  Tyler Nighswander
  Ben Nagy                              Samir Aguiar
  Aidan Thornton                        Aleksandar Nikolich
  Sam Hakim                             Laszlo Szekeres
  David A. Wheeler                      Turo Lamminen
  Andreas Stieger                       Richard Godbee
  Louis Dassy                           teor2345
  Alex Moneger                          Dmitry Vyukov
  Keegan McAllister                     Kostya Serebryany
  Richo Healey                          Martijn Bogaard
  rc0r                                  Jonathan Foote
  Christian Holler                      Dominique Pelle
  Jacek Wielemborek                     Leo Barnes
  Jeremy Barnes                         Jeff Trull
  Guillaume Endignoux                   ilovezfs
  Daniel Godas-Lopez                    Franjo Ivancic
  Austin Seipp                          Daniel Komaromy
  Daniel Binderman                      Jonathan Metzman
  Vegard Nossum                         Jan Kneschke
  Kurt Roeckx                           Marcel Boehme
  Van-Thuan Pham                        Abhik Roychoudhury
  Joshua J. Drake                       Toby Hutton
  Rene Freingruber                      Sergey Davidoff
  Sami Liedes                           Craig Young
  Andrzej Jackowski                     Daniel Hodson
  Nathan Voss                           Dominik Maier
  Andrea Biondo                         Vincent Le Garrec
  Khaled Yakdan                         Kuang-che Wu
  Josephine Calliotte                   Konrad Welc
  Thomas Rooijakkers                    David Carlier
  Ruben ten Hove                        Joey Jiao
  fuzzah                                @intrigus-lgtm
  Yaakov Saxon                          Sergej Schumilo


If you use AFL++ in scientific work, consider citing our paper presented at WOOT'20:

Andrea Fioraldi, Dominik Maier, Heiko Eißfeldt, and Marc Heuse. “AFL++: Combining incremental steps of fuzzing research”. In 14th USENIX Workshop on Offensive Technologies (WOOT 20). USENIX Association, Aug. 2020.
@inproceedings {AFLplusplus-Woot20,
author = {Andrea Fioraldi and Dominik Maier and Heiko Ei{\ss}feldt and Marc Heuse},
title = {{AFL++}: Combining Incremental Steps of Fuzzing Research},
booktitle = {14th {USENIX} Workshop on Offensive Technologies ({WOOT} 20)},
year = {2020},
publisher = {{USENIX} Association},
month = aug,