#fuzzing #testing #security #web


Structure-aware, black box HTTP fuzzing library

1 unstable release

Uses new Rust 2021

0.1.0-rc.0 Sep 3, 2022

#87 in Testing

Download history 21/week @ 2022-09-03 567/week @ 2022-09-10 7/week @ 2022-09-17

595 downloads per month



๐Ÿš€ FeroxFuzz ๐Ÿš€

A structure-aware HTTP fuzzing library

๐Ÿค” Another ferox? why? ๐Ÿค”

Chill, it's not another command-line tool, this one's a library! ๐Ÿ˜

More specifically, FeroxFuzz is a structure-aware HTTP fuzzing library.

The primary goal in writing FeroxFuzz was to move some core pieces out of feroxbuster and into a place where they could be generally useful for other folks. In so doing, my hope is that anyone who wants to write web tooling and/or one-off web fuzzers in Rust, can do so with minimal effort.


FeroxFuzz's overall design is derived from LibAFL. FeroxFuzz implements most of the components listed in LibAFL: A Framework to Build Modular and Reusable Fuzzers (pre-print). When FeroxFuzz deviates, it's typically due to supporting async code.

Similar to LibAFL, FeroxFuzz is a composable fuzzing library. However, unlike LibAFL, FeroxFuzz is solely focused on black box HTTP fuzzing.

๐Ÿšง Warning: Under Construction ๐Ÿšง

FeroxFuzz is very capable, and was made to suit all of my planned needs for a new feroxbuster. However, I still expect FeroxFuzz's API to change, at least slightly, as work on the new version of feroxbuster begins.

Until the API solidifies, breaking changes may will occur.

Getting Started

The easiest way to get started is to include FeroxFuzz in your project's Cargo.toml.

feroxfuzz = { version = "0.1.0-beta" }


In addition to the examples/ folder, the API docs have extensive documentation of components along with examples of their use.

  • FeroxFuzz API Docs: FeroxFuzz's API docs, which are automatically generated from the doc comments in this repo.
  • Official Examples: FeroxFuzz's dedicated, runnable examples, which are great for digging into specific concepts and are heavily commented.


The example below (examples/async-simple.rs) shows the bare minimum to write a fuzzer using FeroxFuzz.

If using the source, the example can be run from the feroxfuzz/ directory using the following command:

note: unless you have a webserver running on your machine @ port 8000, you'll need to change the target passed in Request::from_url

cargo run --example async-simple
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // create a new corpus from the given list of words
    let words = Wordlist::from_file("./examples/words")?

    // pass the corpus to the state object, which will be shared between all of the fuzzers and processors
    let mut state = SharedState::with_corpus(words);

    // bring-your-own client, this example uses the reqwest library
    let req_client = reqwest::Client::builder().build()?;

    // with some client that can handle the actual http request/response stuff
    // we can build a feroxfuzz client, specifically an asynchronous client in this
    // instance.
    // feroxfuzz provides both a blocking and an asynchronous client implementation
    // using reqwest. 
    let client = AsyncClient::with_client(req_client);

    // ReplaceKeyword mutators operate similar to how ffuf/wfuzz work, in that they'll
    // put the current corpus item wherever the keyword is found, as long as its found
    // in data marked fuzzable (see ShouldFuzz directives below)
    let mutator = ReplaceKeyword::new(&"FUZZ", "words");

    // fuzz directives control which parts of the request should be fuzzed
    // anything not marked fuzzable is considered to be static and won't be mutated
    // ShouldFuzz directives map to the various components of an HTTP request
    let request = Request::from_url(
        Some(&[ShouldFuzz::URLParameterValue(b"admin=FUZZ", b"=")]),

    // a `StatusCodeDecider` provides a way to inspect each response's status code and decide upon some Action
    // based on the result of whatever comparison function (closure) is passed to the StatusCodeDecider's
    // constructor
    // in plain english, the `StatusCodeDecider` below will check to see if the request's http response code
    // received is equal to 200/OK. If the response code is 200, then the decider will recommend the `Keep`
    // action be performed. If the response code is anything other than 200, then the recommendation will
    // be to `Discard` the response.
    // `Keep`ing the response means that the response will be allowed to continue on for further processing
    // later in the fuzz loop.
    let decider = StatusCodeDecider::new(200, |status, observed, _state| {
        if status == observed {
        } else {

    // a `ResponseObserver` is responsible for gathering information from each response and providing
    // that information to later fuzzing components, like Processors. It knows things like the response's
    // status code, content length, the time it took to receive the response, and a bunch of other stuff.
    let response_observer: ResponseObserver<AsyncResponse> = ResponseObserver::new();

    // a `ResponseProcessor` provides access to the fuzzer's instance of `ResponseObserver`
    // as well as the `Action` returned from calling `Deciders` (like the `StatusCodeDecider` above).
    // Those two objects may be used to produce side-effects, such as printing, logging, calling out to
    // some other service, or whatever else you can think of.
    let response_printer = ResponseProcessor::new(
        |response_observer: &ResponseObserver<AsyncResponse>, action, _state| {
            if let Some(Action::Keep) = action {
                    "[{}] {} - {} - {:?}",

    // `Scheduler`s manage how the fuzzer gets entries from the corpus. The `OrderedScheduler` provides
    // in-order access of the associated `Corpus` (`Wordlist` in this example's case)
    let scheduler = OrderedScheduler::new(state.clone())?;

    // the macro calls below are essentially boilerplate. Whatever observers, deciders, mutators,
    // and processors you want to use, you simply pass them to the appropriate macro call and
    // eventually to the Fuzzer constructor.
    let deciders = build_deciders!(decider);
    let mutators = build_mutators!(mutator);
    let observers = build_observers!(response_observer);
    let processors = build_processors!(response_printer);

    let threads = 40;  // number of threads to use for the fuzzing process

    // the `Fuzzer` is the main component of the feroxfuzz library. It wraps most of the other components 
    // and takes care of the actual fuzzing process.
    let mut fuzzer = AsyncFuzzer::new(
        threads, client, request, scheduler, mutators, observers, processors, deciders,

    // the fuzzer will run until it iterates over the entire corpus once
    fuzzer.fuzz_once(&mut state).await?;



The fuzzer above would produce something similar to what's shown below.

[200] 815 - http://localhost:8000/?admin=Ajax - 840.985ยตs
[200] 206 - http://localhost:8000/?admin=Al - 4.092037ms
  Rng=RomuDuoJrRand { x_state: 97704, y_state: 403063 }
  Corpus[words]=Wordlist::{len=102774, top-3=[Static("A"), Static("A's"), Static("AMD")]},


~1M SLoC