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afl-utils - набор утилит для упрощения работы с american fuzzy lop

american fuzzy lop - это утилита fuzzy testing. А afl-utils это набор утилит, которые упрощают работу с первым.


Экспериментальная функция:

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afl-utils is a collection of utilities to assist fuzzing with american-fuzzy-lop (afl). afl-utils includes tools for:

  • automated crash sample collection, verification, reduction and analysis (afl-collect, afl-vcrash)
  • easy management of parallel (multi-core) fuzzing jobs (afl-multicore, afl-multikill)
  • corpus optimization (afl-minimize)
  • fuzzer stats supervision (afl-stats)



For installation instructions see docs/INSTALL.md.

In versions 1.03a and 1.04a multi-threading capabilities have been introduced to speed up things. However if you observe some strange behaviour in one of these (or later) versions, please file a bug report (either open an issue here on GH or send it in directly to hlt99 at blinkenshell dot org). The latest non-multi-threading release that comes with all features is 1.02a. So if running the multi-threaded version is somehow troubling for you, you can always git checkout v1.02a after cloning. I might be adding a separate branch for multi-threaded afl-utils releases in the future.


afl-collect basically copies all crash sample files from an afl synchronisation directory (used by multiple afl instances when run in parallel) into a single location providing easy access for further crash analysis. Beyond that afl-collect has some more advanced features like invalid crash sample removing (see afl-vcrash) as well as generating and executing gdb scripts that make use of Exploitable. The purpose of these scripts is to automate crash sample classification (see screenshot below) and reduction.
Version 1.01a introduced crash sample de-duplication using backtrace hashes calculated by exploitable. To use this feature invoke afl-collect with -e <gdb_script> switch for automatic gdb+exploitable script generation and execution. For each backtrace hash only a single crash sample file will be kept.
afl-collect is quite slow when operating on large sample sets and using gdb+exploitable script execution, so be patient!
When invoked with -d <database>, sample information will be stored in the database. This will only be done when the gdb-script execution step is selected (-e). If database is an existing database containing sample info, afl-collect will skip all samples that already have a database entry during sample processing. This will work also when -e is not requested. This makes subsequent afl-collect runs more efficient, since only unseen samples are processed (and added to the database).


            [-h] [-j THREADS] [-m] [-r] [-rr] sync_dir collection_dir target_cmd

afl-collect copies all crash sample files from an afl sync dir used by multiple
fuzzers when fuzzing in parallel into a single location providing easy access
for further crash analysis.

positional arguments:
  sync_dir              afl synchronisation directory crash samples will be
                        collected from.
  collection_dir        Output directory that will hold a copy of all crash
                        samples and other generated files. Existing files in the
                        collection directory will be overwritten!
  target_cmd            Path to the target binary and its command line arguments.
                        Use '@@' to specify crash sample input file position
                        (see afl-fuzz usage).

optional arguments:
  -h, --help            show this help message and exit
                        Submit sample data into an sqlite3 database (only when
                        used together with '-e'). afl-collect skips processing
                        of samples already found in existing database.
  -e GDB_EXPL_SCRIPT_FILE, --execute-gdb-script GDB_EXPL_SCRIPT_FILE
                        Generate and execute a gdb+exploitable script after crash
                        sample collection for crash classification. (Like option
                        '-g', plus script execution.)
                        Writes all collected crash sample filenames into a file
                        in the collection directory.
  -g GDB_SCRIPT_FILE, --generate-gdb-script GDB_SCRIPT_FILE
                        Generate gdb script to run 'exploitable.py' on all
                        collected crash samples. Generated script will be placed
                        into collection directory.
                        Enable parallel analysis by specifying the number of
                        threads afl-collect will utilize.
  -m, --minimize-filenames
                        Minimize crash sample file names by only keeping fuzzer
                        name and ID.
  -r, --remove-invalid  Verify collected crash samples and remove samples that
                        do not lead to crashes or cause timeouts (runs
                        'afl-vcrash -r' on collection directory). This step is
                        done prior to any script file execution or file list
  -rr, --remove-unexploitable
                        Remove crash samples that have an exploitable
                        classification of 'NOT_EXPLOITABLE', 'PROBABLY_NOT_EXPLOITABLE'
                        or 'UNKNOWN'. Sample file removal will take place after
                        gdb+exploitable script execution. Has no effect without '-e'.


Helps to create a minimized corpus from samples of a parallel fuzzing job. It basically works as follows:

  1. Collect all queue samples from an afl synchronisation directory in collection_dir.
  2. Run afl-cmin on the collected corpus, save minimized corpus in collection_dir.cmin.
  3. Run afl-tmin on the remaining samples to reduce them in size. Save results in collection_dir.tmin if step two was omitted or collection_dir.cmin.tmin otherwise.
  4. Perform a "dry-run" for each sample and move crashes/timeouts out of the corpus. This step will be useful prior to starting a new or resuming a parallel fuzzing job on a corpus containing intermittent crashes. Crashes will be moved to a .crashes directory, if one of steps 1, 2 or 3 were performed. If only "dry-run" is requested, crashing samples will be moved from the queue to the crashes dirs within an afl sync dir. For timeouts the behavior is similar: When operating on a collection directory timeouts will be moved to a .hangs directory. When operating on the original afl synchronisation directory timeouts will go into hangs dir within the corresponding afl fuzzer dir.

As already indicated, all these steps are optional, making the tool quite flexible. E.g. running only step four can be handy before resuming a parallel fuzzing session. In order to skip step one, simply provide a directory containing fuzzing samples. Then afl-minimize will not collect any samples, instead afl-cmin and/or afl-tmin are run on the samples in the provided directory.

When operating on corpora with many samples use --tmin with caution. Running thousands of files through afl-tmin can take very long. So make sure the results are as expected and worth the effort. You don't want to waste days of CPU time just to reduce your corpus size by a few bytes, don't you?!

Performing the "dry-run" step after running afl-cmin might seem pointless, but my experience showed that sometimes crashes remain the minimized corpus. So this is just an additional step to get rid of them. But don't expect "dry-run" to always clear your corpus from crashes with a 100% success rate!


afl-minimize [-c COLLECTION_DIR [--cmin [opts]] [--tmin [opts]]] [-d] [-h]
             [-j] sync_dir -- target_cmd

afl-minimize performs several optimization steps to reduce the size of an afl-
fuzz corpus.

positional arguments:
  sync_dir              afl synchronisation directory containing multiple
                        fuzzers and their queues.
  target_cmd            Path to the target binary and its command line
                        arguments. Use '@@' to specify crash sample input file
                        position (see afl-fuzz usage).

optional arguments:
  -h, --help            show this help message and exit
                        Collect all samples from the synchronisation dir and
                        store them in the collection dir. Existing files in
                        the collection directory will be overwritten!
  --cmin                Run afl-cmin on collection dir. Has no effect without
  --cmin-mem-limit CMIN_MEM_LIMIT
                        Set memory limit for afl-cmin.
  --cmin-timeout CMIN_TIMEOUT
                        Set timeout for afl-cmin.
  --tmin                Run afl-tmin on minimized collection dir if used
                        together with '--cmin'or on unoptimized collection dir
                        otherwise. Has no effect without '-c'.
  --tmin-mem-limit TMIN_MEM_LIMIT
                        Set memory limit for afl-tmin.
  --tmin-timeout TMIN_TIMEOUT
                        Set timeout for afl-tmin.
  -d, --dry-run         Perform dry-run on collection dir, if '-c' is provided
                        or on synchronisation dir otherwise. Dry-run will move
                        intermittent crashes out of the corpus.
                        Enable parallel dry-run and t-minimization step by
                        specifying the number of threads afl-minimize will


afl-multicore starts several parallel fuzzing jobs in the background using nohup (Note: So afl's fancy interface is gone). Fuzzer outputs (stdout and stderr) will be redirected to /dev/null. Use --verbose to turn output redirection off. This is particularly useful when debugging afl-fuzz invocations. The auto-generated file nohup.out might also contain some useful info.
Another way to debug afl-fuzz invocations is test mode. Just start afl-multicore and provide the --test flag to perform a test run. afl-multicore will start a single fuzzing instance in interactive mode using a test output directory <out-dir>_test. The interactive setting in your config file will be ignored.
Note: After running a test you will have to clean up the test output directory <out-dir>_test yourself!
Note: For interactive test runs screen is not required!

If you want to check the fuzzers' progress see fuzzer_stats in the respective fuzzer directory in the synchronisation dir (sync_dir/SESSION###/fuzzer_stats)! The master instance files are always located at sync_dir/SESSION000/.
An afl-multicore session can (and should!) easily be aborted with the help of afl-multikill (see below).

If you prefer to work with afl's UI instead of background processes and stat files, screen mode is for you. "Interactive" screen mode can be enabled using the interactive = on directive in the config file (see below). In order to use it, start afl-multicore from inside a screen session. A new screen window is created for every afl instance. Though screen mode is not supported by afl-multikill.
Attention: When using screen mode be sure to set necessary environment variables in the [environment] section of your afl-multicore configuration! Alternatively run screen -X setenv <var_name> <var_value> from inside screen before running afl-multicore. Both ways the environment is inherited by all subsequently created screen windows.


afl-multicore [-c config] [-h] [-t] [-v] <cmd> <jobs>

afl-multicore starts several parallel fuzzing jobs, that are run in the
background. For fuzzer stats see 'out_dir/SESSION###/fuzzer_stats'!

positional arguments:
  cmd                   afl-multicore command to execute: start, resume, add.
  jobs                  Number of instances to start/resume/add.

optional arguments:
  -h, --help            show this help message and exit
                        afl-multicore config file (Default: afl-
  -t, --test            Perform a test run by starting a single afl instance
                        in interactive mode using a test output directory.
  -v, --verbose         For debugging purposes do not redirect stderr/stdout
                        of the created subprocesses to /dev/null (Default:
                        off). Check 'nohup.out' for further outputs.

Target settings and afl options are configured in an INI-like configuration file. The most simple configuration may look something like:

input = ./in
output = ./out

target = ~/bin/target
cmdline = --target-opt

Of course a lot more settings can be configured, some of these settings are:

  • afl options: timeout, memory limit, dictionary, ...
  • job options: session name, interactive mode
  • environment variables for interactive screen mode

For a complete list of options and their descriptions see the included sample configuration file afl-multicore.conf.sample.

To start four fuzzing instances simply do:

$ afl-multicore -c target.conf start 4

Now, if you want to add two more instances because afl-gotcpu states you've got some spare CPU cycles available, use the add command:

$ afl-multicore -c target.conf add 2

Interrupted fuzzing jobs can be resumed the same way using the resume command.
Note: It is possible to tell afl-multicore to resume more jobs for a specific target than were previously started. Obviously afl-multicore can resume just as many afl instances as it finds output directories for! Use the add command to start additional afl instances!

afl-fuzz can be run using its -f <file> argument to specify the location of the generated sample. When using multiple afl-fuzz instances a single file obviously can't do the trick, because multiple fuzzers running in parallel would need separate files to store their data. For that reason afl-multicore extends the provided filename with the instance number similar to the session naming scheme: cur_input would be extended into cur_input_000, cur_input_001 and so on. In order to use these files just use %% in the target command line specification within the config file. afl-multicore will then do all the magic and use the correct files for the different instances of afl-fuzz.

Example config:

target = /your/app/here
cmdline = --some-target-opts --input-file %%
# ^- translates to:
#    --some-target-opts --input-file /path/to/cur_input_000
#    --some-target-opts --input-file /path/to/cur_input_001
#    ...


file = /path/to/cur_input


Aborts all afl-fuzz instances belonging to an active non-interactive afl-multicore session. afl-multicore sessions that were started in screen mode can not be aborted!


afl-multikill [-S SESSION]

afl-multikill aborts all afl-fuzz instances belonging to an active
afl-multicore session. Interactive screen sessions are not supported!

optional arguments:
  -h, --help            show this help message and exit
  -S SESSION, --session SESSION
                        afl-multicore session to abort


Prints fuzzing statistics similar to afl-whatsup -s and posts (tweets) them to Twitter. This is especially useful when fuzzing on multiple machines. Regularly ssh-ing into all of your boxes to check fuzzer_stats quickly becomes a PITA...
For setup instructions, please see docs/INSTALL.md! Screenshots of sample tweets can be found in the final section of this document.


afl-stats [-c]

Post selected contents of fuzzer_stats to Twitter.

optional arguments:
  -h, --help            show this help message and exit
                        afl-stats config file (Default: afl-stats.conf)!


afl-vcrash verifies that afl-fuzz crash samples really lead to crashes in the target binary and optionally removes these samples automatically.
Note: afl-vcrash functionality is incorporated into afl-collect. If afl-collect is invoked with switch -r, it runs afl-vcrash -qr to quietly remove invalid samples from the collected files.
To enable parallel crash sample verification provide -j followed by the desired number of threads afl-vcrash will utilize. Depending on the target process you're fuzzing, running multiple threads in parallel can significantly improve verification speeds.


afl-vcrash [-f LIST_FILENAME] [-h] [-j THREADS] [-q] [-r] [-t TIMEOUT] collection_dir
           target_command [target_command_args]

afl-vcrash verifies that afl-fuzz crash samples lead to crashes in the
target binary.

positional arguments:
  collection_dir        Directory holding all crash samples that will
                        be verified.
  target_command        Target binary including command line options.
                        Use '@@' to specify crash sample input file
                        position (see afl-fuzz usage).

optional arguments:
  -h, --help            show this help message and exit
                        Writes all crash sample file names that do not
                        lead to crashes into a file.
                        Enable parallel verification by specifying the
                        number of threads afl-vcrash will utilize.
  -q, --quiet           Suppress output of crash sample file names that
                        do not lead to crashes. This is particularly
                        useful when combined with '-r' or '-f'.
  -r, --remove          Remove crash samples that do not lead to crashes.
                        Define the timeout in seconds before killing the
                        verification of a crash sample



Sample output:



Sample output (normal mode):





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