fuzz-me-maybe

An environment-variable-based fuzzing harness for Node applications

fuzz-me-maybe is a small harness that makes instrumentation of various network protocols easily. It is a small module that offers some command-line input directly into a radamsa+sinkdweller fuzzing system.

Using fuzz-me-maybe, you can grab an off-the-shelf module (e.g. rhea, mqtt-packet) and instrument it with this wrapper script, which will allow you to interact with the fuzzer from environment variables. This allows you to make fuzzers out of any off-the-shelf node module by hooking/instrumenting it directly, versus needing to rewrite potentially complex upstream logic.

Basic Usage

Basic usage (no custom parameters) is as follows. Take code such as:

function outputToStream(stream, data) {
    stream.write(data);
}

and change it to:

const FuzzMeMaybe = require('fuzz-me-maybe');
let fuzzer = new FuzzMeMaybe();
 
function outputToStream(stream, data) {
    stream.write(fuzzer.maybe(data));
}

Default environment variable control

fuzz-me-maybe turns off the fuzzer by default. This is such that it will allow tests and other systems to run unless there are explicit flags turning on the fuzzer, and lets you leave fuzzing infrastructure in place. To enable your fuzzer, you will need to set $ENVPREFIX_ENABLED=1 on your command line (by default, this environment prefix is FUZZER_, so you would set FUZZER_ENABLED=1 to turn on the fuzzer.)

If you want to show your I/O (for example, to save testcases or a log of fuzz output), you can show it by setting $ENVPREFIX_SHOW_IO=1 on your command line to print to stdout, and $ENVPREFIX_SHOW_IO=1 $ENVPREFIX_SHOW_IO_STDERR=1, where $ENVPREFIX is either FUZZER (the default) or what you set with the registerEnvironmentPrefix method.

Custom environment flags

fuzz-me-maybe allows for boolean, counted, and string matching flags. To get more functionality, tag your fuzzer calls for enable/disable:

const FuzzMeMaybe = require('fuzz-me-maybe');
let fuzzer = new FuzzMeMaybe();
fuzzer.registerEnvironmentPrefix('MYFUZZER_');
fuzzer.registerFlag('output_to_stream', 'boolean', true);
 
function outputToStream(stream, data) {
    stream.write(fuzzer.maybe(data, 'output_to_stream'));
}

Now, all calls with the tag 'output_to_stream' can be turned off on the command line by setting MYFUZZER_OUTPUT_TO_STREAM=0. In this case, the maybe method will no longer fire.

Integer (count) skips

You may also build integer skips:

const FuzzMeMaybe = require('fuzz-me-maybe');
let fuzzer = new FuzzMeMaybe();
fuzzer.registerEnvironmentPrefix('MYFUZZER_');
fuzzer.registerFlag('output_to_stream', 'skip_first', 10);
 
function outputToStream(stream, data) {
    stream.write(fuzzer.maybe(data, 'output_to_stream'));
}

This skip_first flag will now skip the first 10 calls of the output_to_stream flag. To change this, you can set the environment variable MYFUZZER_OUTPUT_TO_STREAM_SKIP_FIRST=20, and then the first 20 calls will be skipped instead.

String skips

Similar to integer skips, you can also register a flag to not allow for specific strings:

const FuzzMeMaybe = require('fuzz-me-maybe');
let fuzzer = new FuzzMeMaybe();
fuzzer.registerEnvironmentPrefix('MYFUZZER_');
fuzzer.registerFlag('output_to_stream', 'skip_string', 'ACCESS_KEY');
 
function outputToStream(stream, data) {
    stream.write(fuzzer.maybe(data, 'output_to_stream'));
}

In this case, if data contains the string ACCESS_KEY, it will not fuzz data. This can be changed on the command line with the environment variable MYFUZZER_OUTPUT_TO_STREAM_SKIP_STRING="POST", for example, to change the skipped string to POST instead.

License

MIT License.