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This document describes the honggfuzz project.


Honggfuzz is a security oriented, feedback-driven, evolutionary, easy-to-use fuzzer with interesting analysis options.


  • It's multi-threaded and multi-process: no need to run multiple copies of your fuzzer, as honggfuzz can unlock potential of all your available CPU cores. The file corpus is shared between threads (and fuzzed instances)
  • It's blazingly fast (specifically in the persistent fuzzing mode). A simple LLVMFuzzerTestOneInput function can be tested with up to 1 mo iterations per second on a relatively modern CPU (e.g. i7-6600K)
  • Has a nice track record of uncovered security bugs: e.g. the only (to the date) vulnerability in OpenSSL with the critical score mark was discovered by honggfuzz
  • Uses low-level interfaces to monitor processes (e.g. ptrace under Linux and NetBSD). As opposed to other fuzzers, it will discover and report hidden signals (caught and potentially hidden by signal handlers)
  • Easy-to-use, feed it a simple input corpus (can even consist of a single, 1-byte file) and it will work its way up expanding it utilizing feedback-based coverage metrics
  • Supports several (more than any other coverage-based feedback-driven fuzzer) hardware-based (CPU: branch/instruction counting, Intel BTS, Intel PT) and software-based feedback-driven fuzzing methods known from other fuzzers (libfuzzer, afl)
  • Works (at least) under GNU/Linux, FreeBSD, NetBSD, Mac OS X, Windows/CygWin and Android
  • Supports persistent fuzzing mode (long-lived process calling a fuzzed API repeatedly) with libhfuzz/libhfuzz.a. More on that can be found here
  • Can fuzz remote/standalone long-lasting processes (e.g. network servers like Apache's httpd and ISC's bind)
  • It comes with the examples directory, consisting of real world fuzz setups for widely-used software (e.g. Apache and OpenSSL)


  • A POSIX compliant operating system, Android or Windows (CygWin)
  • GNU/Linux with modern kernel (>= v4.2) for hardware-based code coverage guided fuzzing
  • A corpus of input files. Honggfuzz expects a set of files to use and modify as input to the application you're fuzzing. How you get or create these files is up to you, but you might be interested in the following sources:
    • Image formats: Tavis Ormandy's Image Testuite has been effective at finding vulnerabilities in various graphics libraries.
    • PDF: Adobe provides some test PDF files.

Note: With the feedback-driven coverage-based modes, you can start your fuzzing with even a single 1-byte file.

Compatibility list

It should work under the following operating systems:

OS Status Notes
GNU/Linux Works ptrace() API (x86, x86-64 disassembly support)
FreeBSD Works POSIX signal interface
NetBSD Works ptrace() API (x86, x86-64 disassembly support)
Mac OS X Works POSIX signal interface/Mac OS X crash reports (x86-64/x86 disassembly support)
Android Works ptrace() API (x86, x86-64 disassembly support)
MS Windows Works POSIX signal interface via CygWin
Other Unices Depends* POSIX signal interface

*) It might work provided that a given operating system implements wait4() call


Usage: ./honggfuzz [options] -- path_to_command [args]
	Help plz..
 --input|-f VALUE
	Path to a directory containing initial file corpus
	Enable persistent fuzzing (use hfuzz_cc/hfuzz-clang to compile code)
	*DEFAULT-MODE-BY-DEFAULT* Enable compile-time instrumentation (use hfuzz_cc/hfuzz-clang to compile code)
	Static mode (dry-mode), disable any instrumentation (hw/sw)
	Don't close children's stdin, stdout, stderr; can be noisy
 --timeout|-t VALUE
	Timeout in seconds (default: '10')
 --threads|-n VALUE
	Number of concurrent fuzzing threads (default: number of CPUs / 2)
	Provide fuzzing input on STDIN, instead of ___FILE___
 --mutations_per_run|-r VALUE
	Maximal number of mutations per one run (default: '6')
 --logfile|-l VALUE
	Log file
	Disable ANSI console; use simple log output
	Enable crashes verifier
 --debug_level|-d VALUE
	Debug level (0 - FATAL ... 4 - DEBUG), (default: '3' [INFO])
 --extension|-e VALUE
	Input file extension (e.g. 'swf'), (default: 'fuzz')
 --workspace|-W VALUE
	Workspace directory to save crashes & runtime files (default: '.')
 --covdir VALUE
	New coverage is written to a separate directory (default: use the input directory)
 --dict|-w VALUE
	Dictionary file. Format:
 --stackhash_bl|-B VALUE
	Stackhashes blacklist file (one entry per line)
 --mutate_cmd|-c VALUE
	External command producing fuzz files (instead of internal mutators)
 --pprocess_cmd VALUE
	External command postprocessing files produced by internal mutators
 --run_time VALUE
	Number of seconds this fuzzing session will last (default: '0' [no limit])
 --iterations|-N VALUE
	Number of fuzzing iterations (default: '0' [no limit])
 --rlimit_as VALUE
	Per process RLIMIT_AS in MiB (default: '0' [no limit])
 --rlimit_rss VALUE
	Per process RLIMIT_RSS in MiB (default: '0' [no limit])
 --rlimit_data VALUE
	Per process RLIMIT_DATA in MiB (default: '0' [no limit])
 --report|-R VALUE
	Write report to this file (default: 'HONGGFUZZ.REPORT.TXT')
 --max_file_size|-F VALUE
	Maximal size of files processed by the fuzzer in bytes (default: '1048576')
	Clear all environment variables before executing the binary
 --env|-E VALUE
	Pass this environment variable, can be used multiple times
	Save all test-cases (not only the unique ones) by appending the current time-stamp to the filenames
	Use SIGVTALRM to kill timeouting processes (default: use SIGKILL)
	Enable sanitizers settings (default: false)
 --monitor_sigabrt VALUE
	Monitor SIGABRT (default: 'false for Android - 'true for other platforms)
 --no_fb_timeout VALUE
	Skip feedback if the process has timeouted (default: 'false')
	Exit upon seeing the first crash (default: 'false')
 --linux_symbols_bl VALUE
	Symbols blacklist filter file (one entry per line)
 --linux_symbols_wl VALUE
	Symbols whitelist filter file (one entry per line)
 --linux_pid|-p VALUE
	Attach to a pid (and its thread group)
 --linux_file_pid VALUE
	Attach to pid (and its thread group) read from file
 --linux_addr_low_limit VALUE
	Address limit (from si.si_addr) below which crashes are not reported, (default: '0')
	Don't disable ASLR randomization, might be useful with MSAN
 --linux_perf_ignore_above VALUE
	Ignore perf events which report IPs above this address
	Use Intel BTS to count unique edges
	Use Intel Processor Trace to count unique blocks (requires
	Gather kernel-only coverage with Intel PT and with Intel BTS
	Use Linux NET namespace isolation
	Use Linux PID namespace isolation
	Use Linux IPC namespace isolation
 --netbsd_symbols_bl VALUE
	Symbols blacklist filter file (one entry per line)
 --netbsd_symbols_wl VALUE
	Symbols whitelist filter file (one entry per line)
 --netbsd_pid|-p VALUE
	Attach to a pid (and its thread group)
 --netbsd_file_pid VALUE
	Attach to pid (and its thread group) read from file
 --netbsd_addr_low_limit VALUE
	Address limit (from si.si_addr) below which crashes are not reported, (default: '0')

 Run the binary over a mutated file chosen from the directory. Disable fuzzing feedback (dry/static mode)
  honggfuzz -f input_dir -x -- /usr/bin/djpeg ___FILE___
 As above, provide input over STDIN:
  honggfuzz -f input_dir -x -s -- /usr/bin/djpeg
 Use compile-time instrumentation (libhfuzz/instrument.c):
  honggfuzz -f input_dir -- /usr/bin/djpeg ___FILE___
 Use persistent mode (libhfuzz/persistent.c) w/o instrumentation:
  honggfuzz -f input_dir -P -x -- /usr/bin/djpeg_persistent_mode
 Use persistent mode (libhfuzz/persistent.c) and compile-time instrumentation:
  honggfuzz -f input_dir -P -- /usr/bin/djpeg_persistent_mode
 Run the binary with dynamically generate inputs, maximize total no. of instructions:
  honggfuzz --linux_perf_instr -- /usr/bin/djpeg ___FILE___
 As above, maximize total no. of branches:
  honggfuzz --linux_perf_branch -- /usr/bin/djpeg ___FILE___
 As above, maximize unique branches (edges) via Intel BTS:
  honggfuzz --linux_perf_bts_edge -- /usr/bin/djpeg ___FILE___
 As above, maximize unique code blocks via Intel Processor Trace (requires
  honggfuzz --linux_perf_ipt_block -- /usr/bin/djpeg ___FILE___


Mode Output file
Linux,NetBSD SIGSEGV.PC.4ba1ae.STACK.13599d485.CODE.1.ADDR.0x10.INSTR.mov____0x10(%rbx),%rax.fuzz
POSIX signal interface SIGSEGV.22758.2010-07-


  • SIGSEGV,SIGILL,SIGBUS,SIGABRT,SIGFPE - Description of the signal which terminated the process (when using ptrace() API, it's a signal which was delivered to the process, even if silently discarded)
  • PC.0x8056ad7 - Program Counter (PC) value (ptrace() API only), for x86 it's a value of the EIP register (RIP for x86-64)
  • STACK.13599d485 - Stack signature (based on stack-tracing)
  • ADDR.0x30333037 - Value of the siginfo_t.si_addr (see man 2 signaction for more details) (most likely meaningless for SIGABRT)
  • INSTR.mov____0x10(%rbx),%rax` - Disassembled instruction which was found under the last known PC (Program Counter) (x86, x86-64 architectures only, meaningless for SIGABRT)


  • Q: Why the name honggfuzz?

  • A: The term honggfuzz was coined during a major and memorable event in the city of Zurich, where a Welsh security celebrity tried to reach Höngg in a cab while singing Another one bites the dust.

  • Q: Why do you prefer the ptrace() API to the POSIX signal interface?

  • A: The ptrace() API is more flexible when it comes to analyzing a process' crash. wait3/4() syscalls are only able to determine the type of signal which crashed an application and limited resource usage information (see man wait4).

  • Q: Why isn't there any support for the ptrace() API when compiling under FreeBSD or Mac OS X operating systems?

  • A: These operating systems lack some specific ptrace() operations, including PT_GETREGS (Mac OS X) and PT_GETSIGINFO, both of which honggfuzz depends on. If you have any ideas on how to get around this limitation, send us an email or patch.


This project is licensed under the Apache License, Version 2.0


  • Thanks to [ Tavis Ormandy] for many valuable ideas used in the course of this project's design and implementation phases
  • Thanks to my 1337 friends for all sorts of support and distraction :) - LiquidK, lcamtuf, novocainated, asiraP, ScaryBeasts, redpig, jln