libafl

SKILL.md

Modular Rust fuzzing library for building custom fuzzers with fine-grained control over feedback, mutation, and execution.

Provides drop-in libFuzzer compatibility mode for existing harnesses, or use as a Rust library to build fully customized fuzzers from scratch

Modular component architecture covers observers (coverage, timing), feedback mechanisms, objectives (crashes, timeouts), mutators, schedulers, and in-process executors

Supports multi-core fuzzing, dictionary-guided mutations, auto token extraction, crash deduplication via backtrace hashing, and text UI for monitoring

Requires LLVM 15-18, Rust toolchain, and compiler wrapper setup for proper instrumentation; includes real-world examples for libpng and CMake projects

LibAFL

LibAFL is a modular fuzzing library that implements features from AFL-based fuzzers like AFL++. Unlike traditional fuzzers, LibAFL provides all functionality in a modular and customizable way as a Rust library. It can be used as a drop-in replacement for libFuzzer or as a library to build custom fuzzers from scratch.

When to Use

Fuzzer
Best For
Complexity

libFuzzer
Quick setup, single-threaded
Low

AFL++
Multi-core, general purpose
Medium

LibAFL
Custom fuzzers, advanced features, research
High

Choose LibAFL when:

You need custom mutation strategies or feedback mechanisms

Standard fuzzers don't support your target architecture

You want to implement novel fuzzing techniques

You need fine-grained control over fuzzing components

You're conducting fuzzing research