aflpp

An agent skill by trailofbits, from trailofbits/skills. Tags: cli, developer-tools, fuzzing, testing.

What it does

Sets up and runs AFL++ for multi-core fuzzing of C/C++ projects built with afl-clang-fast or afl-gcc-fast. Covers instrumentation modes, parallel main and secondary campaigns, persistent mode, corpus minimization, and crash triage. Use when scaling fuzzing across cores, fuzzing a mature C/C++ codebase, reading the afl-fuzz status screen, or moving on after libFuzzer has plateaued.

Install

With the skills CLI, which installs into Claude Code, Codex, Cursor and other agents:

npx skills add trailofbits/skills --skill aflpp

Or copy the skill folder into Claude Code's skills directory by hand (~/.claude/skills for every project, or .claude/skills inside one):

git clone --depth 1 https://github.com/trailofbits/skills
cp -r skills/plugins/testing-handbook-skills/skills/aflpp ~/.claude/skills/aflpp

Safety box score

Grade D, elevated risk: 46 of 100 risk points, rated 2026-10-17. The grade rates what the skill and its scripts can reach on the machine of whoever installs it, across eight categories from shell execution to secrets access. How the score works.

This skill sets up and runs AFL++ fuzzing campaigns, mostly in Docker but with host-side system tuning options. The main risks are privileged container execution, root-required kernel/boot changes that disable mitigations, and fetching tools or headers from external sources.

Category levels, from 0 (none) to 3 (high)
Category	Level	Why
Code & shell execution	2 (moderate)	It runs many shell commands and the wrapper evaluates its arguments with `bash -c "$"` and `bash -c "cd /src && bash -c \"$\""`, giving it real command-execution capability.
Network access	2 (moderate)	It pulls `aflplusplus/aflplusplus:stable` from Docker Hub and downloads `argv-fuzz-inl.h` from `raw.githubusercontent.com`, so external network access is part of the workflow.
Filesystem reach	2 (moderate)	Most actions are scoped to the working tree, but the host-tuning path runs `update-grub` and `reboot`, affecting system configuration beyond the project directory.
Secrets & credentials	0 (none)	The skill does not read key stores, `.env` files, browser sessions, or ask for tokens/passwords.
Privilege & persistence	3 (high)	It uses `docker run --privileged`, and the host tuning steps say `afl-system-config`/`afl-persistent-config` require root, followed by `apt install`, `update-grub`, and `reboot`.
Instruction hijack surface	1 (low)	The wrapper collapses the remaining arguments into shell code with `bash -c`, so quoting is not preserved and shell injection is possible if untrusted text is passed as arguments.
Irreversible actions	1 (low)	It starts background fuzzers, monitors them, and can terminate them with `kill $(jobs -p)`, but it does not post, deploy, or modify external systems.
Transparency	0 (none)	All shipped files are readable text; there are no binaries, blobs, or runtime-decoded code in the skill bundle.

Before installing

Read the wrapper section and decide whether you are comfortable with `--privileged` Docker and root-level tuning.
Use a disposable VM before trying the `afl-system-config` / `afl-persistent-config` steps.
Check whether you need the external `docker pull` / `curl` downloads, and verify them from a trusted source first.

Rated 2026-10-17 by an automated review of 3 files from the skill's repository.

Source

Repository: trailofbits/skills (all skills from this repository)
Path: plugins/testing-handbook-skills/skills/aflpp/SKILL.md
Branch: main
Collection: testing-handbook-skills
Updated: 2026-09-19

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