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A fork and successor of the Sulley Fuzzing Framework

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boofuzz: Network Protocol Fuzzing for Humans Documentation Status Join the chat at

Boofuzz is a fork of and the successor to the venerable Sulley fuzzing framework. Besides numerous bug fixes, boofuzz aims for extensibility. The goal: fuzz everything.

boofuzz screenshot


Sulley has been the preeminent open source fuzzer for some time, but has fallen out of maintenance.


Like Sulley, boofuzz incorporates all the critical elements of a fuzzer:

  • Easy and quick data generation.

  • Instrumentation – AKA failure detection.

  • Target reset after failure.

  • Recording of test data.

Unlike Sulley, boofuzz also features:

  • Online documentation.

  • Support for arbitrary communications mediums.

  • Built-in support for serial fuzzing, ethernet- and IP-layer, UDP broadcast.

  • Better recording of test data – consistent, thorough, clear.

  • Test result CSV export.

  • Extensible instrumentation/failure detection.

  • Much easier install experience!

  • Far fewer bugs.

Sulley is affectionately named after the giant teal and purple creature from Monsters Inc. due to his fuzziness. Boofuzz is likewise named after the only creature known to have scared Sulley himself: Boo!

Boo from Monsters Inc

Boo from Monsters Inc


pip install boofuzz

Boofuzz installs as a Python library used to build fuzzer scripts. See INSTALL.rst for advanced and detailed instructions.


Documentation is available at, including nifty quickstart guides.


Pull requests are welcome, as boofuzz is actively maintained (at the time of this writing ;)). See CONTRIBUTING.rst.


For questions that take the form of “How do I… with boofuzz?” or “I got this error with boofuzz, why?”, consider posting your question on Stack Overflow. Make sure to use the fuzzing tag.

If you’ve found a bug, or have an idea/suggestion/request, file an issue here on GitHub.

For other questions, check out boofuzz on gitter or Google Groups.

For updates, follow @b00fuzz on Twitter.




  • Remove six compatibility module.

  • Remove Python 2 compatibility code.

  • Remove specifying object inheritance in classes.

  • Added Web UI listening on specific IP address.

  • Added Python 3.11 compatibility.


  • Specified encoding on file write rather than assuming default encoding.

  • Changed type of default_value from string to bytes for FromFile.

  • s_update primitive was out of date.

  • The minimum supported Python version is now 3.8.

  • Removed duplicates from BitField primitive.

  • Fixed unwanted deprecation warning when using Session.fuzz(name=name).

  • Changed type of dep_value argument of Block to bytes and added type checks.

  • Split into multiple files.

  • Using poetry as package build system.



  • Added support for fuzzing NETCONF servers with the NETCONFConnection class.

  • Add support and tests for Python 3.10.

  • Added Session arg db_filename to modify the location of the log database.


  • Fixed check for when to enable the web app.

  • Documented the possibility to disable the web app.

  • Correctly initialize all children of a request which inherits from FuzzableBlock.

  • Added type checking for arguments of Bytes primitive to prevent incorrect use.

  • Fixed TypeError in s_binary initialization.

  • Remove redundant unicode strings.



  • Fuzzing CLI – Use main_helper() to use boofuzz’s generic fuzzing CLI with your script.

  • Combinatorial fuzzing – now fuzzes multiple mutations at once by default.

  • Test cases can now be specified and re-run by name.

  • Implemented visual request-graph rendering functions for Session.

  • Added to web UIL: runtime, exec speed, current test case name.

  • Added simple custom checksum and example usage.

  • Added Simple primitive that uses only the specified values for fuzzing.

  • Added Float primitive with support for IEEE 754 encoding.

  • Added an example for s_float/Float usage.


  • Clarified documentation of custom checksum function for Checksum primitive.

  • String and RandomData primitives now use a local and independent instance of random.

  • The minimum supported Python version is now 3.6.

  • Fixed two memory leaks in the fuzz logger.



  • Memory optimization: Efficient mutation generation and smarter string reuse – decrease memory consumption by orders of magnitude.

  • Aligned block: Aligns content length to multiple of certain number of bytes.

  • Relative names: Name references for Checksum, Size, etc. now resolve absolute and relative names. Block and primitive names no longer need to be globally unique within a message, they only need to be locally unique within a block.

  • Passing data between messages: Callbacks now have a TestCaseContext object to which one can save data to be used later in the test case. TestCaseSessionReference can be passed as a default value in a protocol definition. The name it references must have been saved by the time that message in the protocol is reached.

  • Fuzzable rewrite: Simpler definitions for new fuzz primitives. See for an example of a very simple primitive.

  • Protocol definition: Protocols can now be defined with an object oriented rather than static approach.

  • Independent mutation and encoding steps: Will enable multiple mutations and code coverage feedback.

  • Procmon: Additional debug steps. Partial backwards compatibility for old interface.

  • ProcessMonitorLocal allows running procmon as part of fuzzer process.

  • Network monitor: improved network interface discovery (Linux support).

  • Added support for fuzzing Unix sockets with the UnixSocketConnection class.

  • Added metadata to ProtocolSession to support callbacks – current_message, previous_message.

  • All primitive arguments are now optional keyword arguments.


  • Various web interface fixes.

  • Various refactors and simplifications.

  • Fewer duplicates from Group primitives.

  • Network monitor: fixed data_bytes calculation and PcapThread synchronization.

  • Fixed a crash when using the network monitor.

  • Session can now be “quiet” by passing an empty list of loggers.

  • Process Monitor: fixed Thread.isAlive for Python 3.9 compatibility.

  • Correctly truncate values of the string primitive when max_len or size is set.

  • The string primitive will no longer generate duplicates when max_len or size is set.

  • Greatly improved string to bytes conversion speed.



  • Added simple TFTP fuzzer example.


  • Fixed UDPSocketConnection data truncation when sending more data than the socket supports.

  • Fixed execution of procmon stop_commands.

  • Fixed TCP and SSL server connections.



  • Rewrote and split the SocketConnection class into individual classes per socket type.

  • SocketConnection is now deprecated. Use the classes derived from BaseSocketConnection instead.

  • Added support for receiving on raw Layer 2 and Layer 3 connections.

  • Layer 2 and Layer 3 connections may now use arbitrary payload / MTU sizes.

  • Moved connection related modules into new connections submodule.

  • Added the ability to repeat sending of packages within a given time or count.

  • Added optional timeout and threshold to quit infinite connection retries.

  • Reworked Monitors, consolidated interface. Breaking change: session no longer has netmon_options and procmon_options.

  • SessionInfo has had attributes renamed; procmon_results and netmon_results are deprecated and now aliases for monitor_results and monitor_data respectively.

  • New BoofuzzFailure exception type allows callback methods to signal a failure that should halt the current test case.

  • Added capture_output option to process monitor to capture target process stderr/stdout .

  • Added post-start-target callbacks (called every time a target is started or restarted).

  • Added method to gracefully stop PED-RPC Server.

  • Added new boofuzz logo and favicon to docs and webinterface.

  • Added FileConnection to dump messages to files.

  • Removed deprecated session arguments fuzz_data_logger, log_level, logfile, logfile_level and log().

  • Removed deprecated logger FuzzLoggerFile.

  • crc32c is no longer a required package. Install manually if needed.


  • Fixed size of s_size block when output is ascii.

  • Fixed issue with tornado on Python 3.8 and Windows.

  • Fixed various potential type errors.

  • Renamed requests folder to request_definitions because it shadowed the name of the requests python module.

  • Examples are up to date with current Boofuzz version.

  • Modified timings on serial_connection unit tests to improve test reliability.

  • Refactored old unit-tests.

  • Fixed network monitor compatibility with Python 3.

  • Minor console GUI optimizations.

  • Fixed crash_threshold_element handling if blocks are used.

  • Fixed many bugs in which a failure would not stop the test case evaluation.



  • New primitive s_bytes which fuzzes an arbitrary length binary value (similiar to s_string).

  • We are now using Black for code style standardization.

  • Compatibility for Python 3.8

  • Added crc32c as checksum algorithm (Castagnoli).

  • Added favicon for web interface.

  • Pushed Tornado to 5.x and unpinned Flask.


  • Test cases were not being properly closed when using the check_message() functionality.

  • Some code style changes to meet PEP8.

  • s_group primitive was not accepting empty default value.

  • Timeout during opening TCP connection now raises BoofuzzTargetConnectionFailedError exception.

  • SSL/TLS works again. See examples/ and examples/

  • Dropped six.binary_type in favor of b”” format.

  • Fixed process monitor handling of backslashes in Windows start commands.

  • Fixed and documented boo open.

  • Fixed receive function in fuzz_logger_curses.

  • Installing boofuzz with sudo is no longer recommended, use the –user option of pip instead.

  • Fixed setting socket timeout options on Windows.

  • If all sockets are exhausted, repeatedly try fuzzing for 4 minutes before failing.

  • Fixed CSV logger send and receive data decoding.

  • Handle SSL-related exception. Added ignore_connection_ssl_errors session attribute that can be set to True to ignore SSL-related error on a test case.

  • Fixed s_from_file decoding in Python 2 (the encoding parameter is now depreciated).

  • Updated documentation of s_checksum. It is possible to use a custom algorithm with this block.



  • New curses logger class to provide a console gui similar to the webinterface. Use the session option console_gui to enable it. This has not been tested under Windows!

  • Compatibility for Python 3

  • Large test cases are now truncated, unless a failure is detected.

  • When a target fails to respond after restart, boofuzz will now continue to restart instead of crashing.

  • New Session option keep_web_open to allow analyzing the test results after test completion.

  • Process monitor creates new crash file for each run by default.

  • Long lines now wrap in web view; longer lines no longer need to be truncated.

  • Process monitor now stores crash bins in JSON format instead of pickled format.

  • Process monitor in Windows will use taskkill -F if taskkill fails.


  • Web server no longer crashes when asked for a non-existing test case.

  • EINPROGRESS socket error is now handled while opening a socket (note: this sometimes-transient error motivated the move to retry upon connection failure)



  • New Session options restart_callbacks, pre_send_callbacks, and post_test_case_callbacks to hand over custom callback functions.

  • New Session option fuzz_db_keep_only_n_pass_cases. This allowes saving only n test cases preceding a failure or error to the database.

  • Added logic to find next available port for web interface or disable the web interface.

  • Removed sleep logs when sleep time is zero.

  • Added option to reuse the connection to the target.


  • Windows process monitor now handles combination of proc_name and/or start_commands more reasonably

  • Windows process monitor handles certain errors more gracefully

  • Fixed target close behavior so post send callbacks can use the target.

  • Fixed a dependency issue in installation.



  • Socket Connections now allow client fuzzing.

  • Log only the data actually sent, when sending is truncated. Helps reduce database size, especially when fuzzing layer 2 or 3.

  • Target recv function now accepts a max_recv_bytes argument.


  • Fixed install package – now includes JavaScript files.



  • Clearer error message when procmon is unavailable at fuzz start.

  • Web UI now refreshes current case even when snap-to-current-test-case is disabled.


  • Web UI no longer permits negative test cases.

  • Fix Windows procmon regression.

  • Minor fixes and UI tweaks.



  • New boo open command can open and inspect saved database log files.

  • Unix procmon now saves coredumps by default.

  • Improved “Cannot connect to target” error message.

  • Improved API for registering callbacks.

  • Made the global REQUESTS map available in top level boofuzz package.


  • Handle exceptions when opening crash bin files in process monitor.

  • Fix Block.__len__ to account for custom encoder.



  • Web UI
    • Statistics now auto-update.

    • Test case logs now stream on the main page.

    • Cool left & right arrow buttons to move through test case

  • New Session parameter receive_data_after_fuzz. Controls whether to execute a receive step after sending fuzz messages. Defaults to False. This significantly speeds up tests in which the target tends not to respond to invalid messages.


  • Text log output would include double titles, e.g. “Test Step: Test Step: …”



  • Web UI
    • Test case numbers are now clickable and link to test case detail view.

    • Test case details now in color!

  • FuzzLoggerDB
    • Added FuzzLoggerDB to allow querying of test results during and after test run. Saves results in a SQLite file.

    • Added Session.open_test_run() to read test results database from previous test run.

  • New Session.feature_check() method to verify protocol functionality before fuzzing.

  • Process Monitor
    • Unify process monitor command line interface between Unix and Windows.

    • Added procmon option proc_name to support asynchronously started target processes.

    • procmon is now checked for errors before user post_send() is called, reducing redundant error messages.

    • Improved procmon logging.

    • Process monitor gives more helpful error messages when running 64-bit application (unsupported) or when a process is killed before being attached

  • Logging Improvements
    • Target open() and close() operations are now logged.

    • Added some optional debug output from boofuzz runtime.

    • Improve capability and logging of messages’ callback methods.

  • New Session & Connection Options
    • Add Session receive_data_after_each_request option to enable disabling of data receipt after messages are sent.

    • Session skip argument replaced with index_start and index_end.

    • Session now has separate crash thresholds for elements/blocks and nodes/messages.

    • Give SocketConnection separate timeouts for send()/recv().

  • Ease of Use
    • Target.recv() now has a default max_bytes value.

    • Added DEFAULT_PROCMON_PORT constant.

    • Session.post_send()’s sock parameter now deprecated (use target instead).


  • Fixed bug in which failures were not recognized.

  • BitField blocks with ASCII format reported incorrect sizes.

  • Fixed bug in s_update.

  • Handle socket errors that were getting missed.

  • Fixed process monitor logging when providing more or less than 1 stop/start commands.

  • Show graceful error on web requests for non-existent test cases.

  • get_max_udp_size() was crashing in Windows.

  • String padding was not always being applied.

  • String was not accepting unicode strings in value parameter.

  • String was skipping valid mutations and reporting wrong num_mutations() when size parameter was used.

  • Unix and Windows process monitors now share much more code.


  • Added unit tests for BitField.

  • Cleaned up CSS on web pages.

  • Added a unit test to verify restart on failure behavior



  • Test cases now have descriptive names

  • Added Session methods to fuzz a test cae by name: fuzz_by_name and fuzz_single_node_by_path


  • Fixed test case numbers when using fuzz_single_case



  • Set Session check_data_received_each_request to False to disable receive after send.


  • Dosctring format fixes.



  • Add Session ignore_connection_reset parameter to suppress ECONNRESET errors.

  • Add Session ignore_connection_aborted parameter to suppress ECONNABORTED errors.


  • Fix Session class docstring formats.



  • s_size is now fuzzable by default.

  • Add new s_fuzz_list primitive to read fuzz value from files.

  • Add new FuzzLoggerCsv to write log in CSV format


  • Fixed: Add missing dummy value for custom checksum, allowing recursive uses of length/checksum (issue #107)



  • Console output - now with colors!

  • added option to move coredumps for later analysis.

  • The process monitor (procmon) now tracks processes by PID by default rather than searching by name. Therefore, stop_commands and proc_name are no longer required.

  • SIGINT (AKA Ctrl+C) now works to close both boofuzz and (usually).

  • Made Unix procmon more compatible with Windows.

  • Improved procmon debugger error handling, e.g., when running 64-bit apps.

  • Windows procmon now runs even if pydbg fails.

  • Added --help parameter to process monitor.

  • Target class now takes procmon and procmon_options in constructor.

  • Added example fuzz scripts.


  • SIGINT (AKA Ctrl+C) now works to close both boofuzz and (usually).

  • Fixed: The pedrpc module was not being properly included in imports.

  • Made --crash_bin optional (as documented).

  • Improved procmon behavior when certain parameters aren’t given.

  • Improved procmon error handling.

  • Fixed a bug in which the procmon would not properly restart a target that had failed without crashing.



  • Added several command injection strings from fuzzdb.

  • Blocks can now be created and nested using with s_block("my-block"):


  • Fixed pydot import error message



  • Added Request.original_value() function to render the request as if it were not fuzzed. This will help enable reuse of a fuzz definition to generate valid requests.

  • SocketConnection can now send and receive UDP broadcast packets using the udp_broadcast constructor parameter.

  • Target.recv() now logs an entry before receiving data, in order to help debug receiving issues.


  • Maximum UDP payload value was incorrect, causing crashes for tests running over UDP. It now works on some systems, but the maximum value may be too high for systems that set it lower than the maximum possible value, 65507.

  • SocketConnection class now handles more send and receive errors: ECONNABORTED, ECONNRESET, ENETRESET, and ETIMEDOUT.

  • Fixed to not include superfluous packages.


  • Added two exceptions: BoofuzzTargetConnectionReset and BoofuzzTargetConnectionAborted.

  • These two exceptions are handled in and may be thrown by any ITargetConnection implementation.



  • Boofuzz now properly reports crashes detected by the process monitor. It was calling log_info instead of log_fail.

  • Boofuzz will no longer crash, but will rather give a helpful error message, if the target refuses socket connections.

  • Add utils/ to boofuzz/utils, avoiding import errors.

  • Fix procmon argument processing bug.

  • Fix typos in INSTALL.rst.


  • Add Gitter badge to README.

  • Add default sleep_time and fuzz_data_logger for Session to simplify boilerplate.


  • Fixed deployment from 0.0.2.

  • Simplify CONTRIBUTING.rst for automated deployment.

  • tox no longer runs entirely as sudo. The sudo has been moved into tox.ini and is more fine-grained.

  • Reduced default Session.__init__ restart_sleep_time from 5 minutes to 5 seconds.


Continuous deployment with Travis.


  • Added build and PyPI badges.

  • Added CONTRIBUTING.rst.

  • check-manifest now runs in automated build.

  • Travis now deploys to PyPI!



  • Tests now run on tox.

  • Added Google Groups and Twitter link.



  • Missing property setters in boofuzz.request.Request now implemented.

  • Unit tests now pass on Windows.

  • Fixed wheel build issue; boofuzz subpackages were missing.



  • Session constructor param session_filename is now optional.


New features

  • Now on PyPI! pip install boofuzz

  • API is now centralized so all classes are available at top level boofuzz.*

    • This makes it way easier to use. Everything can be used like boofuzz.MyClass instead of boofuzz.my_file.MyClass.

  • Added EzOutletReset class to support restarting devices using an ezOutlet EZ-11b.


  • Target now only takes an ITargetConnection. This separates responsibilities and makes our code more flexible with different kinds of connections.


  • Bugs fixed:

    • helpers.udp_checksum was failing with oversized messages.

    • Missing install requirements.

    • Grammar and spelling.

    • was previously installing around five mostly unwanted packages. Fixed.

    • Removed deprecated unit tests.

    • Removed overly broad exception handling in Session.

    • Checksum.render() for UDP was not handling dependencies properly.

Back-end Improvements

This section took the most work. It has the least visible impact, but all of the refactors enable new features, fixes, and unit tests.

  • Primitives and Blocks:

    • Created IFuzzable which properly defines interface for Block, Request, and all BasePrimitive classes.

    • Made effectively private members actually private.

    • Eliminated exhaust() function. It was used only once and was primarily a convoluted break statement. Now it’s gone. :)

    • Split all block and primitive classes into separate files.

  • Many Unit tests added.


  • Continuous integration with Travis is running!

  • Doc organization improvements.

  • Can now install with extras [dev]

Initial Development Release - 0.0.1-dev1

  • Much easier install experience!

  • Support for arbitrary communications mediums.

    • Added serial communications support.

    • Improved sockets to fuzz at Ethernet and IP layers.

  • Extensible instrumentation/failure detection.

  • Better recording of test data.

    • Records all sent and received data

    • Records errors in human-readable format, in same place as sent/received data.

  • Improved functionality in checksum blocks.

  • Self-referential size and checksum blocks now work.

  • post_send callbacks can now check replies and log failures.

  • Far fewer bugs.

  • Numerous refactors within framework code.

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