created_at2019-07-13 23:04:27.266704
updated_at2021-05-21 18:08:08.617541
descriptionMutation framework for usage in fuzzers
Lander Brandt (landaire)




This crate provides functionality one may find useful while developing a fuzzer. A recent nightly Rust build is required for the specialization feature.

Please consider this crate in "beta" and subject to breaking changes for minor version releases for pre-1.0.


Please refer to the wiki for a high-level overview.

For API documentation:


Lain requires rust nightly builds for specialization support.

Add the following to your Cargo.toml:

lain = "0.2"

Example Usage

extern crate lain;

use lain::prelude::*;
use lain::rand;
use lain::hexdump;

#[derive(Debug, Mutatable, NewFuzzed, BinarySerialize)]
struct MyStruct {
    field_1: u8,

    #[lain(bits = 3)]
    field_2: u8,

    #[lain(bits = 5)]
    field_3: u8,

    #[lain(min = 5, max = 10000)]
    field_4: u32,

    ignored_field: u64,

fn main() {
    let mut mutator = Mutator::new(rand::thread_rng());

    let mut instance = MyStruct::new_fuzzed(&mut mutator, None);

    let mut serialized_data = Vec::with_capacity(instance.serialized_size());
    instance.binary_serialize::<_, BigEndian>(&mut serialized_data);

    println!("{:?}", instance);
    println!("hex representation:\n{}", hexdump(&serialized_data));

    // perform small mutations on the instance
    instance.mutate(&mut mutator, None);

    println!("{:?}", instance);

// Output:
// MyStruct { field_1: 95, field_2: 5, field_3: 14, field_4: 8383, ignored_field: 0 }
// hex representation:
// ------00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
// 0000: 5F 75 00 00 20 BF 00 00 00 00 00 00 00 00         _u...¿........
// MyStruct { field_1: 160, field_2: 5, field_3: 14, field_4: 8383, ignored_field: 0 }

A complete example of a fuzzer and its target can be found in the examples directory. The server is written in C and takes data over a TCP socket, parses a message, and mutates some state. The fuzzer has Rust definitions of the C data structure and will send fully mutated messages to the server and utilizes the Driver object to manage fuzzer threads and state.


This project welcomes contributions and suggestions. Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit

When you submit a pull request, a CLA-bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., label, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact with any additional questions or comments.

License: MIT

Commit count: 0

cargo fmt