AFL (american fuzzy lop)


This is the list of all noteworthy changes made in every public release of the tool. See README for the general instruction manual.

Staying informed

Want to stay in the loop on major new features? Join our mailing list by sending a mail to <>.

Not sure if you should upgrade? The lowest currently recommended version is 2.41b. If you’re stuck on an earlier release, it’s strongly advisable to get on with the times.

Version 2.53b (2019-07-25):

  • No functional changes. Updated some comments and license headers to comply with the open sourcing guidelines and publish the source code on GitHub.

Version 2.52b (2017-11-04):

  • Upgraded QEMU patches from 2.3.0 to 2.10.0. Required troubleshooting several weird issues. All the legwork done by Andrew Griffiths.
  • Added setsid to afl-showmap. See the notes for 2.51b.
  • Added target mode (deferred, persistent, qemu, etc) to fuzzer_stats. Requested by Jakub Wilk.
  • afl-tmin should now save a partially minimized file when Ctrl-C is pressed. Suggested by Jakub Wilk.
  • Added an option for afl-analyze to dump offsets in hex. Suggested by Jakub Wilk.
  • Added support for parameters in Patch by Adam of DC949.

Version 2.51b (2017-08-30):

  • Made afl-tmin call setsid to prevent glibc traceback junk from showing up on the terminal in some distros. Suggested by Jakub Wilk.

Version 2.50b (2017-08-19):

  • Fixed an interesting timing corner case spotted by Jakub Wilk.
  • Addressed a libtokencap / pthreads incompatibility issue. Likewise, spotted by Jakub Wilk.
  • Added a mention of afl-kit and Pythia.
  • Added AFL_FAST_CAL.
  • In-place resume now preserves .synced. Suggested by Jakub Wilk.

Version 2.49b (2017-07-18):

  • Added AFL_TMIN_EXACT to allow path constraint for crash minimization.
  • Added dates for releases (retroactively for all of 2017).

Version 2.48b (2017-07-17):

  • Added AFL_ALLOW_TMP to permit some scripts to run in /tmp.
  • Fixed cwd handling in afl-analyze (similar to the quirk in afl-tmin).
  • Made it possible to point -o and -f to the same file in afl-tmin.

Version 2.47b (2017-07-14):

  • Fixed cwd handling in afl-tmin. Spotted by Jakub Wilk.

Version 2.46b (2017-07-10):

  • libdislocator now supports AFL_LD_NO_CALLOC_OVER for folks who do not want to abort on calloc() overflows.
  • Made a minor fix to libtokencap. Reported by Daniel Stender.
  • Added a small JSON dictionary, inspired on a dictionary done by Jakub Wilk.

Version 2.45b (2017-07-04):

  • Added strstr, strcasestr support to libtokencap. Contributed by Daniel Hodson.
  • Fixed a resumption offset glitch spotted by Jakub Wilk.
  • There are definitely no bugs in afl-showmap -c now.

Version 2.44b (2017-06-28):

  • Added a visual indicator of ASAN / MSAN mode when compiling. Requested by Jakub Wilk.
  • Added support for afl-showmap coredumps (-c). Suggested by Jakub Wilk.
  • Added LD_BIND_NOW=1 for afl-showmap by default. Although not really useful, it reportedly helps reproduce some crashes. Suggested by Jakub Wilk.
  • Added a note about allocator_may_return_null=1 not always working with ASAN. Spotted by Jakub Wilk.

Version 2.43b (2017-06-16):

  • Added AFL_NO_ARITH to aid in the fuzzing of text-based formats. Requested by Jakub Wilk.

Version 2.42b (2017-06-02):

  • Renamed the R() macro to avoid a problem with llvm_mode in the latest versions of LLVM. Fix suggested by Christian Holler.

Version 2.41b (2017-04-12):

  • Addressed a major user complaint related to timeout detection. Timing out inputs are now binned as “hangs” only if they exceed a far more generous time limit than the one used to reject slow paths.

Version 2.40b (2017-04-02):

  • Fixed a minor oversight in the insertion strategy for dictionary words. Spotted by Andrzej Jackowski.
  • Made a small improvement to the havoc block insertion strategy.
  • Adjusted color rules for “is it done yet?” indicators.

Version 2.39b (2017-02-02):

  • Improved error reporting in afl-cmin. Suggested by floyd.
  • Made a minor tweak to trace-pc-guard support. Suggested by kcc.
  • Added a mention of afl-monitor.

Version 2.38b (2017-01-22):

  • Added -mllvm -sanitizer-coverage-block-threshold=0 to trace-pc-guard mode, as suggested by Kostya Serebryany.

Version 2.37b (2017-01-22):

  • Fixed a typo. Spotted by Jakub Wilk.

  • Fixed support for make install when using trace-pc. Spotted by Kurt Roeckx.

  • Switched trace-pc to trace-pc-guard, which should be considerably faster and is less quirky. Kudos to Konstantin Serebryany (and sorry for dragging my feet).

    Note that for some reason, this mode doesn’t perform as well as “vanilla” afl-clang-fast / afl-clang.

Version 2.36b (2017-01-14):

  • Fixed a cosmetic bad free() bug when aborting -S sessions. Spotted by Johannes S.
  • Made a small change to afl-whatsup to sort fuzzers by name.
  • Fixed a minor issue with malloc(0) in libdislocator. Spotted by Rene Freingruber.
  • Changed the clobber pattern in libdislocator to a slightly more reliable one. Suggested by Rene Freingruber.
  • Added a note about THP performance. Suggested by Sergey Davidoff.
  • Added a somewhat unofficial support for running afl-tmin with a baseline “mask” that causes it to minimize only for edges that are unique to the input file, but not to the “boring” baseline. Suggested by Sami Liedes.
  • “Fixed” a getPassName() problem with newer versions of clang. Reported by Craig Young and several other folks.

Yep, I know I have a backlog on several other feature requests. Stay tuned!

Version 2.35b:

  • Fixed a minor cmdline reporting glitch, spotted by Leo Barnes.
  • Fixed a silly bug in libdislocator. Spotted by Johannes Schultz.

Version 2.34b:

  • Added a note about afl-tmin to technical_details.txt.
  • Added support for AFL_NO_UI, as suggested by Leo Barnes.

Version 2.33b:

  • Added code to strip -Wl,-z,defs and -Wl,–no-undefined for afl-clang-fast, since they interfere with -shared. Spotted and diagnosed by Toby Hutton.
  • Added some fuzzing tips for Android.

Version 2.32b:

  • Added a check for AFL_HARDEN combined with AFL_USE_*SAN. Suggested by Hanno Boeck.
  • Made several other cosmetic adjustments to cycle timing in the wake of the big tweak made in 2.31b.

Version 2.31b:

  • Changed havoc cycle counts for a marked performance boost, especially with -S / -d. See the discussion of FidgetyAFL in:!topic/afl-users/fOPeb62FZUg

    While this does not implement the approach proposed by the authors of the CCS paper, the solution is a result of digging into that research; more improvements may follow as I do more experiments and get more definitive data.

Version 2.30b:

  • Made minor improvements to persistent mode to avoid the remote possibility of “no instrumentation detected” issues with very low instrumentation densities.
  • Fixed a minor glitch with a leftover process in persistent mode. Reported by Jakub Wilk and Daniel Stender.
  • Made persistent mode bitmaps a bit more consistent and adjusted the way this is shown in the UI, especially in persistent mode.

Version 2.29b:

  • Made a minor #include fix to llvm_mode. Suggested by Jonathan Metzman.
  • Made cosmetic updates to the docs.

Version 2.28b:

  • Added “life pro tips” to docs/.
  • Moved testcases/_extras/ to dictionaries/ for visibility.
  • Made minor improvements to install scripts.
  • Added an important safety tip.

Version 2.27b:

  • Added libtokencap, a simple feature to intercept strcmp / memcmp and generate dictionary entries that can help extend coverage.
  • Moved libdislocator to its own dir, added README.
  • The demo in experimental/instrumented_cmp is no more.

Version 2.26b:

  • Made a fix for to compile on MacOS X.
  • Added support for DYLD_INSERT_LIBRARIES.

Version 2.25b:

  • Made some cosmetic updates to, renamed one env variable.

Version 2.24b:

  • Added, an experimental, abusive allocator. Try it out with AFL_LD_PRELOAD=/path/to/ when running afl-fuzz.

Version 2.23b:

  • Improved the stability metric for persistent mode binaries. Problem spotted by Kurt Roeckx.
  • Made a related improvement that may bring the metric to 100% for those targets.

Version 2.22b:

  • Mentioned the potential conflicts between MSAN / ASAN and FORTIFY_SOURCE. There is no automated check for this, since some distros may implicitly set FORTIFY_SOURCE outside of the compiler’s argv[].
  • Populated the support for AFL_LD_PRELOAD to all companion tools.
  • Made a change to the handling of ./afl-clang-fast -v. Spotted by Jan Kneschke.

Version 2.21b:

  • Added some crash reporting notes for Solaris in docs/INSTALL, as investigated by Martin Carpenter.
  • Fixed a minor UI mix-up with havoc strategy stats.

Version 2.20b:

  • Revamped the handling of variable paths, replacing path count with a “stability” score to give users a much better signal. Based on the feedback from Vegard Nossum.
  • Made a stability improvement to the syncing behavior with resuming fuzzers. Based on the feedback from Vegard.
  • Changed the UI to include current input bitmap density along with total density. Ditto.
  • Added experimental support for parallelizing -M.

Version 2.19b:

  • Made a fix to make sure that auto CPU binding happens at non-overlapping times.

Version 2.18b:

  • Made several performance improvements to has_new_bits() and classify_counts(). This should offer a robust performance bump with fast targets.

Version 2.17b:

  • Killed the error-prone and manual -Z option. On Linux, AFL will now automatically bind to the first free core (or complain if there are no free cores left).
  • Made some doc updates along these lines.

Version 2.16b:

  • Improved support for older versions of clang (hopefully without breaking anything).
  • Moved version data from Makefile to config.h. Suggested by Jonathan Metzman.

Version 2.15b:

  • Added a README section on looking for non-crashing bugs.
  • Added license data to several boring files. Contributed by Jonathan Metzman.

Version 2.14b:

  • Added FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION as a macro defined when compiling with afl-gcc and friends. Suggested by Kostya Serebryany.
  • Refreshed some of the non-x86 docs.

Version 2.13b:

  • Fixed a spurious build test error with trace-pc and llvm_mode/Makefile. Spotted by Markus Teufelberger.
  • Fixed a cosmetic issue with afl-whatsup. Spotted by Brandon Perry.

Version 2.12b:

  • Fixed a minor issue in afl-tmin that can make alphabet minimization less efficient during passes > 1. Spotted by Daniel Binderman.

Version 2.11b:

  • Fixed a minor typo in instrumented_cmp, spotted by Hanno Eissfeldt.
  • Added a missing size check for deterministic insertion steps.
  • Made an improvement to afl-gotcpu when -Z not used.
  • Fixed a typo in in experimental/. Spotted by Kostya Serebryany.

Version 2.10b:

  • Fixed a minor core counting glitch, reported by Tyler Nighswander.

Version 2.09b:

  • Made several documentation updates.
  • Added some visual indicators to promote and simplify the use of -Z.

Version 2.08b:

  • Added explicit support for -m32 and -m64 for llvm_mode. Inspired by a request from Christian Holler.
  • Added a new benchmarking option, as requested by Kostya Serebryany.

Version 2.07b:

  • Added CPU affinity option (-Z) on Linux. With some caution, this can offer a significant (10%+) performance bump and reduce jitter. Proposed by Austin Seipp.
  • Updated afl-gotcpu to use CPU affinity where supported.
  • Fixed confusing CPU_TARGET error messages with QEMU build. Spotted by Daniel Komaromy and others.

Version 2.06b:

  • Worked around LLVM persistent mode hiccups with -shared code. Contributed by Christian Holler.
  • Added __AFL_COMPILER as a convenient way to detect that something is built under afl-gcc / afl-clang / afl-clang-fast and enable custom optimizations in your code. Suggested by Pedro Corte-Real.
  • Upstreamed several minor changes developed by Franjo Ivancic to allow AFL to be built as a library. This is fairly use-specific and may have relatively little appeal to general audiences.

Version 2.05b:

  • Put __sanitizer_cov_module_init & co behind #ifdef to avoid problems with ASAN. Spotted by Christian Holler.

Version 2.04b:

  • Removed indirect-calls coverage from -fsanitize-coverage (since it’s redundant). Spotted by Kostya Serebryany.

Version 2.03b:

  • Added experimental -fsanitize-coverage=trace-pc support that goes with some recent additions to LLVM, as implemented by Kostya Serebryany. Right now, this is cumbersome to use with common build systems, so the mode remains undocumented.
  • Made several substantial improvements to better support non-standard map sizes in LLVM mode.
  • Switched LLVM mode to thread-local execution tracing, which may offer better results in some multithreaded apps.
  • Fixed a minor typo, reported by Heiko Eissfeldt.
  • Force-disabled symbolization for ASAN, as suggested by Christian Holler.
  • AFL_NOX86 renamed to AFL_NO_X86 for consistency.
  • Added AFL_LD_PRELOAD to allow LD_PRELOAD to be set for targets without affecting AFL itself. Suggested by Daniel Godas-Lopez.

Version 2.02b:

  • Fixed a “lcamtuf can’t count to 16” bug in the havoc stage. Reported by Guillaume Endignoux.

Version 2.01b:

  • Made an improvement to cycle counter color coding, based on feedback from Shai Sarfaty.
  • Added a mention of aflize to sister_projects.txt.
  • Fixed an installation issue with afl-as, as spotted by ilovezfs.

Version 2.00b:

  • Cleaned up color handling after a minor snafu in 1.99b (affecting some terminals).
  • Made minor updates to the documentation.

Version 1.99b:

  • Substantially revamped the output and the internal logic of afl-analyze.
  • Cleaned up some of the color handling code and added support for background colors.
  • Removed some stray files (oops).
  • Updated docs to better explain afl-analyze.

Version 1.98b:

  • Improved to “boring string” detection in afl-analyze.
  • Added technical_details.txt for afl-analyze.

Version 1.97b:

  • Added afl-analyze, a nifty tool to analyze the structure of a file based on the feedback from AFL instrumentation. This is kinda experimental, so field reports welcome.
  • Added a mention of afl-cygwin.
  • Fixed a couple of typos, as reported by Jakub Wilk and others.

Version 1.96b:

  • Added -fpic to CFLAGS for the clang plugin, as suggested by Hanno Boeck.
  • Made another clang change (IRBuilder) suggested by Jeff Trull.
  • Fixed several typos, spotted by Jakub Wilk.
  • Added support for AFL_SHUFFLE_QUEUE, based on discussions with Christian Holler.

Version 1.95b:

  • Fixed a harmless bug when handling -B. Spotted by Jacek Wielemborek.
  • Made the exit message a bit more accurate when AFL_EXIT_WHEN_DONE is set.
  • Added some error-checking for old-style forkserver syntax. Suggested by Ben Nagy.
  • Switched from exit() to _exit() in injected code to avoid snafus with destructors in C++ code. Spotted by sunblate.
  • Made a change to avoid spuriously setting __AFL_SHM_ID when AFL_DUMB_FORKSRV is set in conjunction with -n. Spotted by Jakub Wilk.

Version 1.94b:

  • Changed allocator alignment to improve support for non-x86 systems (now that llvm_mode makes this more feasible).
  • Fixed a minor typo in afl-cmin. Spotted by Jonathan Neuschafer.
  • Fixed an obscure bug that would affect people trying to use afl-gcc with $TMP set but $TMPDIR absent. Spotted by Jeremy Barnes.

Version 1.93b:

  • Hopefully fixed a problem with MacOS X and persistent mode, spotted by Leo Barnes.

Version 1.92b:

  • Made yet another C++ fix (namespaces). Reported by Daniel Lockyer.

Version 1.91b:

  • Made another fix to make 1.90b actually work properly with C++ (d’oh). Problem spotted by Daniel Lockyer.

Version 1.90b:

  • Fixed a minor typo spotted by Kai Zhao; and made several other minor updates to docs.
  • Updated the project URL for python-afl. Requested by Jakub Wilk.
  • Fixed a potential problem with deferred mode signatures getting optimized out by the linker (with –gc-sections).

Version 1.89b:

  • Revamped the support for persistent and deferred forkserver modes. Both now feature simpler syntax and do not require companion env variables. Suggested by Jakub Wilk.
  • Added a bit more info about afl-showmap. Suggested by Jacek Wielemborek.

Version 1.88b:

  • Made AFL_EXIT_WHEN_DONE work in non-tty mode. Issue spotted by Jacek Wielemborek.

Version 1.87b:

  • Added QuickStartGuide.txt, a one-page quick start doc.
  • Fixed several typos spotted by Dominique Pelle.
  • Revamped several parts of README.

Version 1.86b:

  • Added support for AFL_SKIP_CRASHES, which is a very hackish solution to the problem of resuming sessions with intermittently crashing inputs.
  • Removed the hard-fail terminal size check, replaced with a dynamic warning shown in place of the UI. Based on feedback from Christian Holler.
  • Fixed a minor typo in show_stats. Spotted by Dingbao Xie.

Version 1.85b:

  • Fixed a garbled sentence in notes on parallel fuzzing. Thanks to Jakub Wilk.
  • Fixed a minor glitch in afl-cmin. Spotted by Jonathan Foote.

Version 1.84b:

  • Made SIMPLE_FILES behave as expected when naming backup directories for crashes and hangs.
  • Added the total number of favored paths to fuzzer_stats. Requested by Ben Nagy.
  • Made afl-tmin, afl-fuzz, and afl-cmin reject negative values passed to -t and -m, since they generally won’t work as expected.
  • Made a fix for no lahf / sahf support on older versions of FreeBSD. Patch contributed by Alex Moneger.

Version 1.83b:

  • Fixed a problem with xargs -d on non-Linux systems in afl-cmin. Spotted by teor2345 and Ben Nagy.
  • Fixed an implicit declaration in LLVM mode on MacOS X. Reported by Kai Zhao.

Version 1.82b:

  • Fixed a harmless but annoying race condition in persistent mode - signal delivery is a bit more finicky than I thought.
  • Updated the documentation to explain persistent mode a bit better.

Version 1.81b:

  • Added persistent mode for in-process fuzzing. See llvm_mode/README.llvm. Inspired by Kostya Serebryany and Christian Holler.
  • Changed the in-place resume code to preserve crashes/README.txt. Suggested by Ben Nagy.
  • Included a potential fix for LLVM mode issues on MacOS X, based on the investigation done by teor2345.

Version 1.80b:

  • Made afl-cmin tolerant of whitespaces in filenames. Suggested by Jonathan Neuschafer and Ketil Froyn.
  • Added support for AFL_EXIT_WHEN_DONE, as suggested by Michael Rash.

Version 1.79b:

  • Added support for dictionary levels, see testcases/README.testcases.
  • Reworked the SQL dictionary to use levels.
  • Added a note about Preeny.

Version 1.78b:

  • Added a dictionary for PDF, contributed by Ben Nagy.
  • Added several references to afl-cov, a new tool by Michael Rash.
  • Fixed a problem with crash reporter detection on MacOS X, as reported by Louis Dassy.

Version 1.77b:

  • Extended the -x option to support single-file dictionaries.
  • Replaced factory-packaged dictionaries with file-based variants.
  • Removed newlines from HTML keywords in testcases/_extras/html/.

Version 1.76b:

  • Very significantly reduced the number of duplicate execs during deterministic checks, chiefly in int16 and int32 stages. Confirmed identical path yields. This should improve early-stage efficiency by around 5-10%.
  • Reduced the likelihood of duplicate non-deterministic execs by bumping up lowest stacking factor from 1 to 2. Quickly confirmed that this doesn’t seem to have significant impact on coverage with libpng.
  • Added a note about integrating afl-fuzz with third-party tools.

Version 1.75b:

  • Improved argv_fuzzing to allow it to emit empty args. Spotted by Jakub Wilk.
  • afl-clang-fast now defines __AFL_HAVE_MANUAL_INIT. Suggested by Jakub Wilk.
  • Fixed a libtool-related bug with afl-clang-fast that would make some ./configure invocations generate incorrect output. Spotted by Jakub Wilk.
  • Removed flock() on Solaris. This means no locking on this platform, but so be it. Problem reported by Martin Carpenter.
  • Fixed a typo. Reported by Jakub Wilk.

Version 1.74b:

  • Added an example argv[] fuzzing wrapper in experimental/argv_fuzzing. Reworked the bash example to be faster, too.
  • Clarified llvm_mode prerequisites for FreeBSD.
  • Improved afl-tmin to use /tmp if cwd is not writeable.
  • Removed redundant includes for sys/fcntl.h, which caused warnings with some nitpicky versions of libc.
  • Added a corpus of basic HTML tags that parsers are likely to pay attention to (no attributes).
  • Added EP_EnabledOnOptLevel0 to llvm_mode, so that the instrumentation is inserted even when AFL_DONT_OPTIMIZE=1 is set.
  • Switched qemu_mode to use the newly-released QEMU 2.3.0, which contains a couple of minor bugfixes.

Version 1.73b:

  • Fixed a bug in effector maps that could sometimes cause AFL to fuzz slightly more than necessary; and in very rare circumstances, could lead to SEGV if eff_map is aligned with page boundary and followed by an unmapped page. Spotted by Jonathan Gray.

Version 1.72b:

  • Fixed a glitch in non-x86 install, spotted by Tobias Ospelt.
  • Added a minor safeguard to llvm_mode Makefile following a report from Kai Zhao.

Version 1.71b:

  • Fixed a bug with installed copies of AFL trying to use QEMU mode. Spotted by G.M. Lime.
  • Added last path / crash / hang times to fuzzer_stats, suggested by Richard Hipp.
  • Fixed a typo, thanks to Jakub Wilk.

Version 1.70b:

  • Modified resumption code to reuse the original timeout value when resuming a session if -t is not given. This prevents timeout creep in continuous fuzzing.
  • Added improved error messages for failed handshake when AFL_DEFER_FORKSRV is set.
  • Made a slight improvement to llvm_mode/Makefile based on feedback from Jakub Wilk.
  • Refreshed several bits of documentation.
  • Added a more prominent note about the MacOS X trade-offs to Makefile.

Version 1.69b:

  • Added support for deferred initialization in LLVM mode. Suggested by Richard Godbee.

Version 1.68b:

  • Fixed a minor PRNG glitch that would make the first seconds of a fuzzing job deterministic. Thanks to Andreas Stieger.
  • Made tmp[] static in the LLVM runtime to keep Valgrind happy (this had no impact on anything else). Spotted by Richard Godbee.
  • Clarified the footnote in README.

Version 1.67b:

  • Made one more correction to llvm_mode Makefile, spotted by Jakub Wilk.

Version 1.66b:

  • Added CC / CXX support to llvm_mode Makefile. Requested by Charlie Eriksen.
  • Fixed ‘make clean’ with gmake. Suggested by Oliver Schneider.
  • Fixed ‘make -j n clean all’. Suggested by Oliver Schneider.
  • Removed build date and time from banners to give people deterministic builds. Requested by Jakub Wilk.

Version 1.65b:

  • Fixed a snafu with some leftover code in afl-clang-fast.
  • Corrected even moar typos.

Version 1.64b:

  • Further simplified afl-clang-fast runtime by reverting .init_array to __attribute__((constructor(0)). This should improve compatibility with non-ELF platforms.
  • Fixed a problem with afl-clang-fast and -shared libraries. Simplified the code by getting rid of .preinit_array and replacing it with a .comm object. Problem reported by Charlie Eriksen.
  • Removed unnecessary instrumentation density adjustment for the LLVM mode. Reported by Jonathan Neuschafer.

Version 1.63b:

  • Updated cgroups_asan/ with a new version from Sam, made a couple changes to streamline it and keep parallel afl instances in separate groups.
  • Fixed typos, thanks to Jakub Wilk.

Version 1.62b:

  • Improved the handling of -x in afl-clang-fast,
  • Improved the handling of low AFL_INST_RATIO settings for QEMU and LLVM modes.
  • Fixed the llvm-config bug for good (thanks to Tobias Ospelt).

Version 1.61b:

  • Fixed an obscure bug compiling OpenSSL with afl-clang-fast. Patch by Laszlo Szekeres.
  • Fixed a ‘make install’ bug on non-x86 systems, thanks to Tobias Ospelt.
  • Fixed a problem with half-broken llvm-config on Odroid, thanks to Tobias Ospelt. (There is another odd bug there that hasn’t been fully fixed - TBD).

Version 1.60b:

  • Allowed experimental/llvm_instrumentation/ to graduate to llvm_mode/.
  • Removed experimental/arm_support/, since it’s completely broken and likely unnecessary with LLVM support in place.
  • Added ASAN cgroups script to experimental/asan_cgroups/, updated existing docs. Courtesy Sam Hakim and David A. Wheeler.
  • Refactored afl-tmin to reduce the number of execs in common use cases. Ideas from Jonathan Neuschafer and Turo Lamminen.
  • Added a note about CLAs at the bottom of README.
  • Renamed testcases_readme.txt to README.testcases for some semblance of consistency.
  • Made assorted updates to docs.
  • Added MEM_BARRIER() to afl-showmap and afl-tmin, just to be safe.

Version 1.59b:

  • Imported Laszlo Szekeres’ experimental LLVM instrumentation into experimental/llvm_instrumentation. I’ll work on including it in the “mainstream” version soon.
  • Fixed another typo, thanks to Jakub Wilk.

Version 1.58b:

  • Added a workaround for abort() behavior in -lpthread programs in QEMU mode. Spotted by Aidan Thornton.
  • Made several documentation updates, including links to the static instrumentation tool (sister_projects.txt).

Version 1.57b:

  • Fixed a problem with exception handling on some versions of MacOS X. Spotted by Samir Aguiar and Anders Wang Kristensen.
  • Tweaked afl-gcc to use BIN_PATH instead of a fixed string in help messages.

Version 1.56b:

  • Renamed related_work.txt to historical_notes.txt.
  • Made minor edits to the ASAN doc.
  • Added docs/sister_projects.txt with a list of inspired or closely related utilities.

Version 1.55b:

  • Fixed a glitch with afl-showmap opening /dev/null with O_RDONLY when running in quiet mode. Spotted by Tyler Nighswander.

Version 1.54b:

  • Added another postprocessor example for PNG.
  • Made a cosmetic fix to realloc() handling in experimental/post_library/, suggested by Jakub Wilk.
  • Improved -ldl handling. Suggested by Jakub Wilk.

Version 1.53b:

  • Fixed an -l ordering issue that is apparently still a problem on Ubuntu. Spotted by William Robinet.

Version 1.52b:

  • Added support for file format postprocessors. Requested by Ben Nagy. This feature is intentionally buried, since it’s fairly easy to misuse and useful only in some scenarios. See experimental/post_library/.

Version 1.51b:

  • Made it possible to properly override LD_BIND_NOW after one very unusual report of trouble.
  • Cleaned up typos, thanks to Jakub Wilk.
  • Fixed a bug in AFL_DUMB_FORKSRV.

Version 1.50b:

  • Fixed a flock() bug that would prevent dir reuse errors from kicking in every now and then.
  • Renamed references to ppvm (the project is now called recidivm).
  • Made improvements to file descriptor handling to avoid leaving some fds unnecessarily open in the child process.
  • Fixed a typo or two.

Version 1.49b:

  • Added code to save original command line in fuzzer_stats and crashes/README.txt. Also saves fuzzer version in fuzzer_stats. Requested by Ben Nagy.

Version 1.48b:

  • Fixed a bug with QEMU fork server crashes when translation is attempted after a jump to an invalid pointer in the child process (i.e., after bumping into a particularly nasty security bug in the tested binary). Reported by Tyler Nighswander.

Version 1.47b:

  • Fixed a bug with afl-cmin in -Q mode complaining about binary being not instrumented. Thanks to Jonathan Neuschafer for the bug report.
  • Fixed another bug with argv handling for afl-fuzz in -Q mode. Reported by Jonathan Neuschafer.
  • Improved the use of colors when showing crash counts in -C mode.

Version 1.46b:

  • Improved instrumentation performance on 32-bit systems by getting rid of xor-swap (oddly enough, xor-swap is still faster on 64-bit) and tweaking alignment.
  • Made path depth numbers more accurate with imported test cases.

Version 1.45b:

  • Added support for SIMPLE_FILES in config.h for folks who don’t like descriptive file names. Generates very simple names without colons, commas, plus signs, dashes, etc.
  • Replaced zero-sized files with symlinks in the variable behavior state dir to simplify examining the relevant test cases.
  • Changed the period of limited-range block ops from 5 to 10 minutes based on a couple of experiments. The basic goal of this delay timer behavior is to better support jobs that are seeded with completely invalid files, in which case, the first few queue cycles may be completed very quickly without discovering new paths. Should have no effect on well-seeded jobs.
  • Made several minor updates to docs.

Version 1.44b:

  • Corrected two bungled attempts to get the -C mode work properly with afl-cmin (accounting for the short-lived releases tagged 1.42 and 1.43b) - sorry.
  • Removed AFL_ALLOW_CRASHES in favor of the -C mode in said tool.
  • Said goodbye to Hello Kitty, as requested by Padraig Brady.

Version 1.41b:

  • Added AFL_ALLOW_CRASHES=1 to afl-cmin. Allows crashing inputs in the output corpus. Changed the default behavior to disallow it.
  • Made the afl-cmin output dir default to 0700, not 0755, to be consistent with afl-fuzz; documented the rationale for 0755 in afl-plot.
  • Lowered the output dir reuse time limit to 25 minutes as a dice-roll compromise after a discussion on afl-users@.
  • Made afl-showmap accept -o /dev/null without borking out.
  • Added support for crash / hang info in exit codes of afl-showmap.
  • Tweaked block operation scaling to also factor in ballpark run time in cases where queue passes take very little time.
  • Fixed typos and made improvements to several docs.

Version 1.40b:

  • Switched to smaller block op sizes during the first passes over the queue. Helps keep test cases small.
  • Added memory barrier for run_target(), just in case compilers get smarter than they are today.
  • Updated a bunch of docs.

Version 1.39b:

  • Added the ability to skip inputs by sending SIGUSR1 to the fuzzer.
  • Reworked several portions of the documentation.
  • Changed the code to reset splicing perf scores between runs to keep them closer to intended length.
  • Reduced the minimum value of -t to 5 for afl-fuzz (~200 exec/sec) and to 10 for auxiliary tools (due to the absence of a fork server).
  • Switched to more aggressive default timeouts (rounded up to 25 ms versus 50 ms - ~40 execs/sec) and made several other cosmetic changes to the timeout code.

Version 1.38b:

  • Fixed a bug in the QEMU build script, spotted by William Robinet.
  • Improved the reporting of skipped bitflips to keep the UI counters a bit more accurate.
  • Cleaned up related_work.txt and added some non-goals.
  • Fixed typos, thanks to Jakub Wilk.

Version 1.37b:

  • Added effector maps, which detect regions that do not seem to respond to bitflips and subsequently exclude them from more expensive steps (arithmetics, known ints, etc). This should offer significant performance improvements with quite a few types of text-based formats, reducing the number of deterministic execs by a factor of 2 or so.
  • Cleaned up mem limit handling in afl-cmin.
  • Switched from uname -i to uname -m to work around Gentoo-specific issues with coreutils when building QEMU. Reported by William Robinet.
  • Switched from PID checking to flock() to detect running sessions. Problem, against all odds, bumped into by Jakub Wilk.
  • Added SKIP_COUNTS and changed the behavior of COVERAGE_ONLY in config.h. Useful only for internal benchmarking.
  • Made improvements to UI refresh rates and exec/sec stats to make them more stable.
  • Made assorted improvements to the documentation and to the QEMU build script.
  • Switched from perror() to strerror() in error macros, thanks to Jakub Wilk for the nag.
  • Moved afl-cmin back to bash, wasn’t thinking straight. It has to stay on bash because other shells may have restrictive limits on array sizes.

Version 1.36b:

  • Switched afl-cmin over to /bin/sh. Thanks to Jonathan Gray.
  • Fixed an off-by-one bug in queue limit check when resuming sessions (could cause NULL ptr deref if you are really unlucky).
  • Fixed the QEMU script to tolerate i686 if returned by uname -i. Based on a problem report from Sebastien Duquette.
  • Added multiple references to Jakub’s ppvm tool.
  • Made several minor improvements to the Makefile.
  • Believe it or not, fixed some typos. Thanks to Jakub Wilk.

Version 1.35b:

  • Cleaned up regular expressions in some of the scripts to avoid errors on *BSD systems. Spotted by Jonathan Gray.

Version 1.34b:

  • Performed a substantial documentation and program output cleanup to better explain the QEMU feature.

Version 1.33b:

  • Added support for AFL_INST_RATIO and AFL_INST_LIBS in the QEMU mode.
  • Fixed a stack allocation crash in QEMU mode (bug in QEMU, fixed with an extra patch applied to the downloaded release).
  • Added code to test the QEMU instrumentation once the afl-qemu-trace binary is built.
  • Modified afl-tmin and afl-showmap to search $PATH for binaries and to better handle QEMU support.
  • Added a check for instrumented binaries when passing -Q to afl-fuzz.

Version 1.32b:

  • Fixed ‘make install’ following the QEMU changes. Spotted by Hanno Boeck.
  • Fixed EXTRA_PAR handling in afl-cmin.

Version 1.31b:

  • Hallelujah! Thanks to Andrew Griffiths, we now support very fast, black-box instrumentation of binary-only code. See qemu_mode/README.qemu.

    To use this feature, you need to follow the instructions in that directory and then run afl-fuzz with -Q.

Version 1.30b:

  • Added -s (summary) option to afl-whatsup. Suggested by Jodie Cunningham.
  • Added a sanity check in afl-tmin to detect minimization to zero len or excess hangs.
  • Fixed alphabet size counter in afl-tmin.
  • Slightly improved the handling of -B in afl-fuzz.
  • Fixed process crash messages with -m none.

Version 1.29b:

  • Improved the naming of test cases when orig: is already present in the file name.
  • Made substantial improvements to technical_details.txt.

Version 1.28b:

  • Made a minor tweak to the instrumentation to preserve the directionality of tuples (i.e., A -> B != B -> A) and to maintain the identity of tight loops (A -> A). You need to recompile targeted binaries to leverage this.
  • Cleaned up some of the afl-whatsup stats.
  • Added several sanity checks to afl-cmin.

Version 1.27b:

  • Made afl-tmin recursive. Thanks to Hanno Boeck for the tip.
  • Added docs/technical_details.txt.
  • Changed afl-showmap search strategy in afl-cmap to just look into the same place that afl-cmin is executed from. Thanks to Jakub Wilk.
  • Removed current_todo.txt and cleaned up the remaining docs.

Version 1.26b:

  • Added total execs/sec stat for afl-whatsup.
  • afl-cmin now auto-selects between cp or ln. Based on feedback from Even Huus.
  • Fixed a typo. Thanks to Jakub Wilk.
  • Made afl-gotcpu a bit more accurate by using getrusage instead of times. Thanks to Jakub Wilk.
  • Fixed a memory limit issue during the build process on NetBSD-current. Reported by Thomas Klausner.

Version 1.25b:

  • Introduced afl-whatsup, a simple tool for querying the status of local synced instances of afl-fuzz.
  • Added -x compiler to clang options on Darwin. Suggested by Filipe Cabecinhas.
  • Improved exit codes for afl-gotcpu.
  • Improved the checks for -m and -t values in afl-cmin. Bug report from Evan Huus.

Version 1.24b:

  • Introduced afl-getcpu, an experimental tool to empirically measure CPU preemption rates. Thanks to Jakub Wilk for the idea.

Version 1.23b:

  • Reverted one change to afl-cmin that actually made it slower.

Version 1.22b:

  • Reworked afl-showmap.c to support normal options, including -o, -q, -e. Also added support for timeouts and memory limits.
  • Made changes to afl-cmin and other scripts to accommodate the new semantics.
  • Officially retired AFL_EDGES_ONLY.
  • Fixed another typo in afl-tmin, courtesy of Jakub Wilk.

Version 1.21b:

  • Graduated to afl-cmin. It is now a first-class utility bundled with the fuzzer.
  • Made significant improvements to afl-cmin to make it faster, more robust, and more versatile.
  • Refactored some of afl-tmin code to make it a bit more readable.
  • Made assorted changes to the doc to document afl-cmin and other stuff.

Version 1.20b:

  • Added AFL_DUMB_FORKSRV, as requested by Jakub Wilk. This works only in -n mode and allows afl-fuzz to run with “dummy” fork servers that don’t output any instrumentation, but follow the same protocol.
  • Renamed AFL_SKIP_CHECKS to AFL_SKIP_BIN_CHECK to make it at least somewhat descriptive.
  • Switched to using clang as the default assembler on MacOS X to work around Xcode issues with newer builds of clang. Testing and patch by Nico Weber.
  • Fixed a typo (via Jakub Wilk).

Version 1.19b:

  • Improved exec failure detection in afl-fuzz and afl-showmap.
  • Improved Ctrl-C handling in afl-showmap.
  • Added afl-tmin, a handy instrumentation-enabled minimizer.

Version 1.18b:

  • Fixed a serious but short-lived bug in the resumption behavior introduced in version 1.16b.
  • Added -t nn+ mode for soft-skipping timing-out paths.

Version 1.17b:

  • Fixed a compiler warning introduced in 1.16b for newer versions of GCC. Thanks to Jakub Wilk and Ilfak Guilfanov.
  • Improved the consistency of saving fuzzer_stats, bitmap info, and auto-dictionaries when aborting fuzzing sessions.
  • Made several noticeable performance improvements to deterministic arith and known int steps.

Version 1.16b:

  • Added a bit of code to make resumption pick up from the last known offset in the queue, rather than always rewinding to the start. Suggested by Jakub Wilk.
  • Switched to tighter timeout control for slow programs (3x rather than 5x average exec speed at init).

Version 1.15b:

  • Added support for AFL_NO_VAR_CHECK to speed up resumption and inhibit variable path warnings for some programs.
  • Made the trimmer run even for variable paths, since there is no special harm in doing so and it can be very beneficial if the trimming still pans out.
  • Made the UI a bit more descriptive by adding “n/a” instead of “0” in a couple of corner cases.

Version 1.14b:

  • Added a (partial) dictionary for JavaScript.
  • Added AFL_NO_CPU_RED, as suggested by Jakub Wilk.
  • Tweaked the havoc scaling logic added in 1.12b.

Version 1.13b:

  • Improved the performance of by switching to a sort-based approach.
  • Made several minor revisions to the docs.

Version 1.12b:

  • Made an improvement to dictionary generation to avoid runs of identical bytes.
  • Added havoc cycle scaling to help with slow binaries in -d mode. Based on a thread with Sami Liedes.
  • Added AFL_SYNC_FIRST for afl-fuzz. This is useful for those who obsess over stats, no special purpose otherwise.
  • Switched to more robust box drawing codes, suggested by Jakub Wilk.
  • Created faster 64-bit variants of several critical-path bitmap functions (sorry, no difference on 32 bits).
  • Fixed moar typos, as reported by Jakub Wilk.

Version 1.11b:

  • Added a bit more info about dictionary strategies to the status screen.

Version 1.10b:

  • Revised the dictionary behavior to use insertion and overwrite in deterministic steps, rather than just the latter. This improves coverage with SQL and the like.
  • Added a mention of “*” in status_screen.txt, as suggested by Jakub Wilk.

Version 1.09b:

  • Corrected a cosmetic problem with ‘extras’ stage count not always being accurate in the stage yields view.
  • Fixed a typo reported by Jakub Wilk and made some minor documentation improvements.

Version 1.08b:

  • Fixed a div-by-zero bug in the newly-added code when using a dictionary.

Version 1.07b:

  • Added code that automatically finds and extracts syntax tokens from the input corpus.
  • Fixed a problem with ld dead-code removal option on MacOS X, reported by Filipe Cabecinhas.
  • Corrected minor typos spotted by Jakub Wilk.
  • Added a couple of more exotic archive format samples.

Version 1.06b:

  • Switched to slightly more accurate (if still not very helpful) reporting of short read and short write errors. These theoretically shouldn’t happen unless you kill the forkserver or run out of disk space. Suggested by Jakub Wilk.
  • Revamped some of the allocator and debug code, adding comments and cleaning up other mess.
  • Tweaked the odds of fuzzing non-favored test cases to make sure that baseline coverage of all inputs is reached sooner.

Version 1.05b:

  • Added a dictionary for WebP.
  • Made some additional performance improvements to, getting deeper into the bash woods.

Version 1.04b:

  • Made substantial performance improvements to with large datasets, albeit at the expense of having to switch back to bash (other shells may have limits on array sizes, etc).
  • Tweaked afl-showmap to support the format used by the new script.

Version 1.03b:

  • Added code to skip README.txt in the input directory to make the crash exploration mode work better. Suggested by Jakub Wilk.
  • Added a dictionary for SQLite.

Version 1.02b:

  • Reverted the ./ search path in because people did not like it.
  • Added very explicit warnings not to run various shell scripts that read or write to /tmp/ (since this is generally a pretty bad idea on multi-user systems).
  • Added a check for /tmp binaries and -f locations in afl-fuzz.

Version 1.01b:

  • Added dictionaries for XML and GIF.

Version 1.00b:

  • Slightly improved the performance of, especially on Linux.
  • Made a couple of improvements to calibration timeouts for resumed scans.

Version 0.99b:

  • Fixed to work with dash, as suggested by Jakub Wilk.
  • Modified to try locate afl-showmap in $PATH and ./. The first part requested by Jakub Wilk.
  • Added support for afl-as –version, as required by one funky build script. Reported by William Robinet.

Version 0.98b:

  • Added a dictionary for TIFF.
  • Fixed another cosmetic snafu with stage exec counts for -x.
  • Switched afl-plot to /bin/sh, since it seems bashism-free. Also tried to remove any obvious bashisms from other experimental/ scripts, most notably including and Requested by Jonathan Gray.

Version 0.97b:

  • Fixed cosmetic issues around the naming of -x strategy files.
  • Added a dictionary for JPEG.
  • Fixed a very rare glitch when running instrumenting 64-bit code that makes heavy use of xmm registers that are also touched by glibc.

Version 0.96b:

  • Added support for extra dictionaries, provided testcases/_extras/png/ as a demo.
  • Fixed a minor bug in number formatting routines used by the UI.
  • Added several additional PNG test cases that are relatively unlikely to be hit by chance.
  • Fixed afl-plot syntax for gnuplot 5.x. Reported by David Necas.

Version 0.95b:

  • Cleaned up the OSX ReportCrash code. Thanks to Tobias Ospelt for help.
  • Added some extra tips for AFL_NO_FORKSERVER on OSX.
  • Refreshed the INSTALL file.

Version 0.94b:

  • Added in-place resume (-i-) to address a common user complaint.
  • Added an awful workaround for ReportCrash on MacOS X. Problem spotted by Joseph Gentle.

Version 0.93b:

  • Fixed the link() workaround, as reported by Jakub Wilk.

Version 0.92b:

  • Added support for reading test cases from another filesystem. Requested by Jakub Wilk.
  • Added pointers to the mailing list.
  • Added a sample PDF document.

Version 0.91b:

  • Refactored to make it a bit more user-friendly and to select for smallest files, not largest bitmaps. Offers a modest corpus size improvement in most cases.
  • Slightly improved the performance of splicing code.

Version 0.90b:

  • Moved to an algorithm where paths are marked as preferred primarily based on size and speed, rather than bitmap coverage. This should offer noticeable performance gains in many use cases.
  • Refactored path calibration code; calibration now takes place as soon as a test case is discovered, to facilitate better prioritization decisions later on.
  • Changed the way of marking variable paths to avoid .state metadata inconsistencies.
  • Made sure that calibration routines always create a new test case to avoid hypothetical problems with utilities that modify the input file.
  • Added bitmap saturation to fuzzer stats and plot data.
  • Added a testcase for JPEG XR.
  • Added a tty check for the colors warning in Makefile, to keep distro build logs tidy. Suggested by Jakub Wilk.

Version 0.89b:

  • Renamed to afl-plot, as requested by Padraig Brady.
  • Improved the compatibility of afl-plot with older versions of gnuplot.
  • Added banner information to fuzzer_stats, populated it to afl-plot.

Version 0.88b:

  • Added support for plotting, with design and implementation based on a prototype design proposed by Michael Rash. Huge thanks!
  • Added, which allows you to, well, generate a nice plot using this data.
  • Refactored the code slightly to make more frequent updates to fuzzer_stats and to provide more detail about synchronization.
  • Added an fflush(stdout) call for non-tty operation, as requested by Joonas Kuorilehto.
  • Added some detail to fuzzer_stats for parity with plot_file.

Version 0.87b:

  • Added support for MSAN, via AFL_USE_MSAN, same gotchas as for ASAN.

Version 0.86b:

  • Added AFL_NO_FORKSRV, allowing the forkserver to be bypassed. Suggested by Ryan Govostes.
  • Simplified afl-showmap.c to make use of the no-forkserver mode.
  • Made minor improvements to, as suggested by Jakub Wilk.

Version 0.85b:

  • Fixed the CPU counting code - no sysctlbyname() on OpenBSD, d’oh. Bug reported by Daniel Dickman.
  • Made a slight correction to error messages - the advice on testing with ulimit was a tiny bit off by a factor of 1024.

Version 0.84b:

  • Added support for the CPU widget on some non-Linux platforms (I hope). Based on feedback from Ryan Govostes.
  • Cleaned up the changelog (very meta).

Version 0.83b:

  • Added experimental/clang_asm_normalize/ and related notes in env_variables.txt and afl-as.c. Thanks to Ryan Govostes for the idea.
  • Added advice on hardware utilization in README.

Version 0.82b:

  • Made additional fixes for Xcode support, juggling -Q and -q flags. Thanks to Ryan Govostes.
  • Added a check for __asm__ blocks and switches to .intel_syntax in assembly. Based on feedback from Ryan Govostes.

Version 0.81b:

  • A workaround for Xcode 6 as -Q flag glitch. Spotted by Ryan Govostes.
  • Improved Solaris build instructions, as suggested by Martin Carpenter.
  • Fix for a slightly busted path scoring conditional. Minor practical impact.

Version 0.80b:

  • Added a check for $PATH-induced loops. Problem noticed by Kartik Agaram.
  • Added AFL_KEEP_ASSEMBLY for easier troubleshooting.
  • Added an override for AFL_USE_ASAN if set at afl compile time. Requested by Hanno Boeck.

Version 0.79b:

  • Made minor adjustments to path skipping logic.
  • Made several documentation updates to reflect the path selection changes made in 0.78b.

Version 0.78b:

  • Added a CPU governor check. Bug report from Joe Zbiciak.

  • Favored paths are now selected strictly based on new edges, not hit counts. This speeds up the first pass by a factor of 3-6x without significantly impacting ultimate coverage (tested with libgif, libpng, libjpeg).

    It also allows some performance & memory usage improvements by making some of the in-memory bitmaps much smaller.

  • Made multiple significant performance improvements to bitmap checking functions, plus switched to a faster hash.

  • Owing largely to these optimizations, bumped the size of the bitmap to 64k and added a warning to detect older binaries that rely on smaller bitmaps.

Version 0.77b:

  • Added AFL_SKIP_CHECKS to bypass binary checks when really warranted. Feature requested by Jakub Wilk.
  • Fixed a couple of typos.
  • Added a warning for runs that are aborted early on.

Version 0.76b:

  • Incorporated another signal handling fix for Solaris. Suggestion submitted by Martin Carpenter.

Version 0.75b:

  • Implemented a slightly more “elegant” kludge for the %llu glitch (see types.h).
  • Relaxed CPU load warnings to stay in sync with reality.

Version 0.74b:

  • Switched to more responsive exec speed averages and better UI speed scaling.
  • Fixed a bug with interrupted reads on Solaris. Issue spotted by Martin Carpenter.

Version 0.73b:

  • Fixed a stray memcpy() instead of memmove() on overlapping buffers. Mostly harmless but still dumb. Mistake spotted thanks to David Higgs.

Version 0.72b:

  • Bumped map size up to 32k. You may want to recompile instrumented binaries (but nothing horrible will happen if you don’t).
  • Made huge performance improvements for bit-counting functions.
  • Default optimizations now include -funroll-loops. This should have interesting effects on the instrumentation. Frankly, I’m just going to ship it and see what happens next. I have a good feeling about this.
  • Made a fix for stack alignment crash on MacOS X 10.10; looks like the rhetorical question in the comments in afl-as.h has been answered. Tracked down by Mudge Zatko.

Version 0.71b:

  • Added a fix for the nonsensical MacOS ELF check. Spotted by Mudge Zatko.
  • Made some improvements to ASAN checks.

Version 0.70b:

  • Added explicit detection of ASANified binaries.
  • Fixed compilation issues on Solaris. Reported by Martin Carpenter.

Version 0.69b:

  • Improved the detection of non-instrumented binaries.
  • Made the crash counter in -C mode accurate.
  • Fixed an obscure install bug that made afl-as non-functional with the tool installed to /usr/bin instead of /usr/local/bin. Found by Florian Kiersch.
  • Fixed for a cosmetic SIGFPE when Ctrl-C is pressed while the fork server is spinning up.

Version 0.68b:

  • Added crash exploration mode! Woot!

Version 0.67b:

  • Fixed several more typos, the project is now cartified 100% typo-free. Thanks to Thomas Jarosch and Jakub Wilk.
  • Made a change to write fuzzer_stats early on.
  • Fixed a glitch when (not!) running on MacOS X as root. Spotted by Tobias Ospelt.
  • Made it possible to override -O3 in Makefile. Suggested by Jakub Wilk.

Version 0.66b:

  • Fixed a very obscure issue with build systems that use gcc as an assembler for hand-written .s files; this would confuse afl-as. Affected nss, reported by Hanno Boeck.
  • Fixed a bug when cleaning up synchronized fuzzer output dirs. Issue reported by Thomas Jarosch.

Version 0.65b:

  • Cleaned up shell printf escape codes in Makefile. Reported by Jakub Wilk.
  • Added more color to fuzzer_stats, provided short documentation of the file format, and made several other stats-related improvements.

Version 0.64b:

  • Enabled GCC support on MacOS X.

Version 0.63b:

  • Provided a new, simplified way to pass data in files (@@). See README.
  • Made additional fixes for 64-bit MacOS X, working around a crashing bug in their linker (umpf) and several other things. It’s alive!
  • Added a minor workaround for a bug in 64-bit FreeBSD (clang -m32 -g doesn’t work on that platform, but clang -m32 does, so we no longer insert -g).
  • Added a build-time warning for inverse video terminals and better instructions in status_screen.txt.

Version 0.62b:

  • Made minor improvements to the allocator, as suggested by Tobias Ospelt.
  • Added example instrumented memcmp() in experimental/instrumented_cmp.
  • Added a speculative fix for MacOS X (clang detection, again).
  • Fixed typos in parallel_fuzzing.txt. Problems spotted by Thomas Jarosch.

Version 0.61b:

  • Fixed a minor issue with clang detection on systems with a clang cc wrapper, so that afl-gcc doesn’t confuse it with GCC.
  • Made cosmetic improvements to docs and to the CPU load indicator.
  • Fixed a glitch with crash removal (README.txt left behind, d’oh).

Version 0.60b:

  • Fixed problems with jump tables generated by exotic versions of GCC. This solves an outstanding problem on OpenBSD when using afl-gcc + PIE (not present with afl-clang).
  • Fixed permissions on one of the sample archives.
  • Added a lahf / sahf workaround for OpenBSD (their assembler doesn’t know about these opcodes).
  • Added docs/INSTALL.

Version 0.59b:

  • Modified ‘make install’ to also install test cases.
  • Provided better pointers to installed README in afl-fuzz.
  • More work on RLIMIT_AS for OpenBSD.

Version 0.58b:

  • Added a core count check on Linux.
  • Refined the code for the lack-of-RLIMIT_AS case on OpenBSD.
  • Added a rudimentary CPU utilization meter to help with optimal loading.

Version 0.57b:

  • Made fixes to support FreeBSD and OpenBSD: use_64bit is now inferred if not explicitly specified when calling afl-as, and RLIMIT_AS is behind an #ifdef. Thanks to Fabian Keil and Jonathan Gray for helping troubleshoot this.
  • Modified ‘make install’ to also install docs (in /usr/local/share/doc/afl).
  • Fixed a typo in status_screen.txt.
  • Made a couple of Makefile improvements as proposed by Jakub Wilk.

Version 0.56b:

  • Added probabilistic instrumentation density reduction in ASAN mode. This compensates for ASAN-specific branches in a crude but workable way.
  • Updated notes_for_asan.txt.

Version 0.55b:

  • Implemented smarter out_dir behavior, automatically deleting directories that don’t contain anything of special value. Requested by several folks, including Hanno Boeck.
  • Added more detail in fuzzer_stats (start time, run time, fuzzer PID).
  • Implemented support for configurable install prefixes in Makefile ($PREFIX), as requested by Luca Barbato.
  • Made it possible to resume by doing -i <out_dir>, without having to specify -i <out_dir>/queue/.

Version 0.54b:

  • Added a fix for -Wformat warning messages (oops, I thought this had been in place for a while).

Version 0.53b:

  • Redesigned the crash & hang duplicate detection code to better deal with fault conditions that can be reached in a multitude of ways.

    The old approach could be compared to hashing stack traces to de-dupe crashes, a method prone to crash count inflation. The alternative I wanted to avoid would be equivalent to just looking at crash %eip, which can have false negatives in common functions such as memcpy().

    The middle ground currently used in afl-fuzz can be compared to looking at every line item in the stack trace and tagging crashes as unique if we see any function name that we haven’t seen before (or if something that we have always seen there suddenly disappears). We do the comparison without paying any attention to ordering or hit counts. This can still cause some crash inflation early on, but the problem will quickly taper off. So, you may get 20 dupes instead of 5,000.

  • Added a fix for harmless but absurd trim ratios shown if the first exec in the trimmer timed out. Spotted by @EspenGx.

Version 0.52b:

  • Added a quick summary of the contents in experimental/.

  • Made a fix to the process of writing fuzzer_stats.

  • Slightly reorganized the .state/ directory, now recording redundant paths, too. Note that this breaks the ability to properly resume older sessions - sorry about that.

    (To fix this, simply move “<out_dir>/.state/” from an older run to <out_dir>/.state/deterministic_done/.)

Version 0.51b:

  • Changed the search order for afl-as to avoid the problem with older copies installed system-wide; this also means that I can remove the Makefile check for that.
  • Made it possible to set instrumentation ratio of 0%.
  • Introduced some typos, fixed others.
  • Fixed the test_prev target in Makefile, as reported by Ozzy Johnson.

Version 0.50b:

  • Improved the ‘make install’ logic, as suggested by Padraig Brady.
  • Revamped various bits of the documentation, especially around perf_tips.txt; based on the feedback from Alexander Cherepanov.
  • Added AFL_INST_RATIO to afl-as. The only case where this comes handy is ffmpeg, at least as far as I can tell. (Trivia: the current version of ffmpeg ./configure also ignores CC and –cc, probably unintentionally).
  • Added documentation for all environmental variables (env_variables.txt).
  • Implemented a visual warning for excessive or insufficient bitmap density.
  • Changed afl-gcc to add -O3 by default; use AFL_DONT_OPTIMIZE if you don’t like that. Big speed gain for ffmpeg, so seems like a good idea.
  • Made a regression fix to afl-as to ignore .LBB labels in gcc mode.

Version 0.49b:

  • Fixed more typos, as found by Jakub Wilk.
  • Added support for clang!
  • Changed AFL_HARDEN to not include ASAN by default. Use AFL_USE_ASAN if needed. The reasons for this are in notes_for_asan.txt.
  • Switched from configure auto-detection to isatty() to keep afl-as and afl-gcc quiet.
  • Improved installation process to properly create symlinks, rather than copies of binaries.

Version 0.48b:

  • Improved afl-fuzz to force-set ASAN_OPTIONS=abort_on_error=1. Otherwise, ASAN crashes wouldn’t be caught at all. Reported by Hanno Boeck.
  • Improved Makefile mkdir logic, as suggested by Hanno Boeck.
  • Improved the 64-bit instrumentation to properly save r8-r11 registers in the x86 setup code. The old behavior could cause rare problems running without instrumentation when the first function called in a particular .o file has 5+ parameters. No impact on code running under afl-fuzz or afl-showmap. Issue spotted by Padraig Brady.

Version 0.47b:

  • Fixed another Makefile bug for parallel builds of afl. Problem identified by Richard W. M. Jones.
  • Added support for suffixes for -m.
  • Updated the documentation and added notes_for_asan.txt. Based on feedback from Hanno Boeck, Ben Laurie, and others.
  • Moved the project to

Version 0.46b:

  • Cleaned up Makefile dependencies for parallel builds. Requested by Richard W. M. Jones.
  • Added support for DESTDIR in Makefile. Once again suggested by Richard W. M. Jones :-)
  • Removed all the USE_64BIT stuff; we now just auto-detect compilation mode. As requested by many callers to the show.
  • Fixed rare problems with programs that use snippets of assembly and switch between .code32 and .code64. Addresses a glitch spotted by Hanno Boeck with compiling ToT gdb.

Version 0.45b:

  • Implemented a test case trimmer. Results in 20-30% size reduction for many types of work loads, with very pronounced improvements in path discovery speeds.
  • Added better warnings for various problems with input directories.
  • Added a Makefile warning for older copies, based on counterintuitive behavior observed by Hovik Manucharyan.
  • Added fuzzer_stats file for status monitoring. Suggested by @dronesec.
  • Fixed moar typos, thanks to Alexander Cherepanov.
  • Implemented better warnings for ASAN memory requirements, based on calls from several angry listeners.
  • Switched to saner behavior with non-tty stdout (less output generated, no ANSI art).

Version 0.44b:

  • Added support for AFL_CC and AFL_CXX, based on a patch from Ben Laurie.
  • Replaced afl-fuzz -S -D with -M for simplicity.
  • Added a check for .section .text; lack of this prevented main() from getting instrumented for some users. Reported by Tom Ritter.
  • Reorganized the testcases/ directory.
  • Added an extra check to confirm that the build is operational.
  • Made more consistent use of color reset codes, as suggested by Oliver Kunz.

Version 0.43b:

  • Fixed a bug with 64-bit gcc -shared relocs.
  • Removed echo -e from Makefile for compatibility with dash. Suggested by Jakub Wilk.
  • Added status_screen.txt.
  • Added experimental/canvas_harness.
  • Made a minor change to the Makefile GCC check. Suggested by Hanno Boeck.

Version 0.42b:

  • Fixed a bug with red zone handling for 64-bit (oops!). Problem reported by Felix Groebert.
  • Implemented horribly experimental ARM support in experimental/arm_support.
  • Made several improvements to error messages.
  • Added AFL_QUIET to silence afl-gcc and afl-as when using wonky build systems. Reported by Hanno Boeck.
  • Improved check for 64-bit compilation, plus several sanity checks in Makefile.

Version 0.41b:

  • Fixed a fork served bug for processes that call execve().
  • Made minor compatibility fixes to Makefile, afl-gcc; suggested by Jakub Wilk.
  • Fixed to work with the new layout of output directories. Suggested by Jakub Wilk.
  • Made multiple performance-related improvements to the injected instrumentation.
  • Added visual indication of the number of imported paths.
  • Fixed afl-showmap to make it work well with new instrumentation.
  • Added much better error messages for crashes when importing test cases or otherwise calibrating the binary.

Version 0.40b:

  • Added support for parallelized fuzzing. Inspired by earlier patch from Sebastian Roschke.
  • Added an example in experimental/distributed_fuzzing/.

Version 0.39b:

  • Redesigned status screen, now 90% more spiffy.
  • Added more verbose and user-friendly messages for some common problems.
  • Modified the resumption code to reconstruct path depth.
  • Changed the code to inhibit core dumps and improve the ability to detect SEGVs.
  • Added a check for redirection of core dumps to programs.
  • Made a minor improvement to the handling of variable paths.
  • Made additional performance tweaks to afl-fuzz, chiefly around mem limits.
  • Added performance_tips.txt.

Version 0.38b:

  • Fixed an fd leak and +cov tracking bug resulting from changes in 0.37b.
  • Implemented auto-scaling for screen update speed.
  • Added a visual indication when running in non-instrumented mode.

Version 0.37b:

  • Added fuzz state tracking for more seamless resumption of aborted fuzzing sessions.
  • Removed the -D option, as it’s no longer necessary.
  • Refactored calibration code and improved startup reporting.
  • Implemented dynamically scaled timeouts, so that you don’t need to play with -t except in some very rare cases.
  • Added visual notification for slow binaries.
  • Improved instrumentation to explicitly cover the other leg of every branch.

Version 0.36b:

  • Implemented fork server support to avoid the overhead of execve(). A nearly-verbatim design from Jann Horn; still pending part 2 that would also skip initial setup steps (thinking about reliable heuristics now).
  • Added a check for shell scripts used as fuzz targets.
  • Added a check for fuzz jobs that don’t seem to be finding anything.
  • Fixed the way IGNORE_FINDS works (was a bit broken after adding splicing and path skip heuristics).

Version 0.35b:

  • Properly integrated 64-bit instrumentation into afl-as.

Version 0.34b:

  • Added a new exec count classifier (the working theory is that it gets meaningful coverage with fewer test cases spewed out).

Version 0.33b:

  • Switched to new, somewhat experimental instrumentation that tries to target only arcs, rather than every line. May be fragile, but is a lot faster (2x+).
  • Made several other cosmetic fixes and typo corrections, thanks to Jakub Wilk.

Version 0.32b:

  • Another take at fixing the C++ exception thing. Reported by Jakub Wilk.

Version 0.31b:

  • Made another fix to afl-as to address a potential problem with newer versions of GCC (introduced in 0.28b). Thanks to Jann Horn.

Version 0.30b:

  • Added more detail about the underlying operations in file names.

Version 0.29b:

  • Made some general improvements to chunk operations.

Version 0.28b:

  • Fixed C++ exception handling in newer versions of GCC. Problem diagnosed by Eberhard Mattes.
  • Fixed the handling of the overflow flag. Once again, thanks to Eberhard Mattes.

Version 0.27b:

  • Added prioritization of new paths over the already-fuzzed ones.
  • Included spliced test case ID in the output file name.
  • Fixed a rare, cosmetic null ptr deref after Ctrl-C.
  • Refactored the code to make copies of test cases in the output directory.
  • Switched to better output file names, keeping track of stage and splicing sources.

Version 0.26b:

  • Revamped storage of testcases, -u option removed,
  • Added a built-in effort minimizer to get rid of potentially redundant inputs,
  • Provided a testcase count minimization script in experimental/,
  • Made miscellaneous improvements to directory and file handling.
  • Fixed a bug in timeout detection.

Version 0.25b:

  • Improved count-based instrumentation.
  • Improved the hang deduplication logic.
  • Added -cov prefixes for test cases.
  • Switched from readdir() to scandir() + alphasort() to preserve ordering of test cases.
  • Added a splicing strategy.
  • Made various minor UI improvements and several other bugfixes.

Version 0.24b:

  • Added program name to the status screen, plus the -T parameter to go with it.

Version 0.23b:

  • Improved the detection of variable behaviors.
  • Added path depth tracking,
  • Improved the UI a bit,
  • Switched to simplified (XOR-based) tuple instrumentation.

Version 0.22b:

  • Refactored the handling of long bitflips and some swaps.
  • Fixed the handling of gcc -pipe, thanks to anonymous reporter.

Version 0.21b (2013-11-12):

  • Initial public release.