atheris

npx skills add trailofbits/skills --skill atheris --agent claude-code

Same command for any agent — swap --agent for codex, cursor, copilot.

# Atheris Atheris is a coverage-guided Python fuzzer built on libFuzzer. It enables fuzzing of both pure Python code and Python C extensions with integrated AddressSanitizer support for detecting memory corruption issues. ## When to Use | Fuzzer | Best For | Complexity | |--------|----------|------------| | Atheris | Python code and C extensions | Low-Medium | | Hypothesis | Property-based testing | Low | | python-afl | AFL-style fuzzing | Medium | **Choose Atheris when:** - Fuzzing pure Python code with coverage guidance - Testing Python C extensions for memory corruption - Integration with libFuzzer ecosystem is desired - AddressSanitizer support is needed ## Quick Start ```python import sys import atheris @atheris.instrument_func def test_one_input(data: bytes): if len(data) == 4: if data[0] == 0x46: # "F" if data[1] == 0x55: # "U" if data[2] == 0x5A: # "Z" if data[3] == 0x5A: # "Z" raise RuntimeError("You caught me") def main(): atheris.Setup(sys.argv, test_one_input) atheris.Fuzz() if __name__ == "__main__": main() ``` Run: ```bash python fuzz.py ``` ## Installation Atheris supports 32-bit and 64-bit Linux, and macOS. We recommend fuzzing on Linux because it's simpler to manag

python fuzz.py
uv pip install atheris
docker build -t atheris .
docker run -it atheris
python -c "import atheris; print(atheris.__version__)"
export CC="clang"
export CFLAGS="-fsanitize=address,fuzzer-no-link"
export CXX="clang++"
export CXXFLAGS="-fsanitize=address,fuzzer-no-link"
export LDSHARED="clang -shared"