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Anthropic's vulnerability harness — 7,270 stars on a repo that says it is not maintained
This is the reference implementation behind Anthropic's "using LLMs to secure source code" work, and it is more complete than the star count suggests you would get. Two halves: interactive Claude Code skills that only read and write files — /threat-model, /vuln-scan, /triage, /patch, /customize, plus /dnr-hunt and /dnr-respond for chasing attacker campaigns through logs — and an autonomous pipeline that actually executes the target and therefore wants a gVisor sandbox. The pipeline is seven stages: build the target into a Docker image with ASAN, run a recon agent that proposes input-parsing subsystems to attack separately, fan out N agents in isolated containers crafting malformed inputs until a crash reproduces 3-for-3, hand it to a grader agent that must reproduce the crash in a fresh container before it crosses over, dedupe against prior findings with a judge, write an exploitability report, then patch — where the grader validates that the build still works, the PoC no longer crashes, tests pass, and a fresh agent cannot bypass the fix. You can pin every subagent with CLAUDE_CODE_SUBAGENT_MODEL.
It is at the top of this list because of what it says about itself. "This harness is a reference, not a product." "This repo is not maintained and is not accepting contributions." And the disclosure that matters: "Autonomous triage and patching are still open issues, and this reference harness doesn't fully solve them... Many partners have reported these steps as their current bottlenecks." That is a vendor naming the two stages between "a fuzzer found a crash" and "a human fixed something" as the unsolved ones, in the repository that exists to demonstrate solving them, while linking to Claude Security — the hosted product that does this for money. There are no published CVEs, no false-positive rate, no benchmark, nothing you could grade it by; the only empirical note in the whole README is a warning that step one is pure static review, so "expect more false positives on any non-canary targets," and that on the deliberately vulnerable demo target /triage may dismiss the scan's own findings because entry.c announces itself as demo code. Worth flagging that GitHub's API reports the license as NOASSERTION and the LICENSE file is plain Apache-2.0 — the fifth time this quarter the badge has been the unreliable half, and the fourth time in the honest direction.
Reach for it if you maintain C or C++ with a parser in it and want a real fuzzing loop scaffolded by someone who has run one. Delete your ad-hoc "point an agent at the repo and ask for vulns" prompt, which is the step this thing proves is the easy part. Tradeoffs: memory bugs in C and C++ only by default, and porting is a /customize slash command rather than a supported path; needs Docker plus gVisor, so this is not a laptop afternoon; unmaintained by declaration and no releases or tags at all; 43 watchers against 7,270 stars and 583 forks, and the contributor graph is four people with 29 commits between them; it crossed our pool on 06-05 at front-page level and again today at 176 stars a day, so a repo that has not been pushed since 06 August is having its second discovery rather than its launch; and the thing it demonstrates best is that the expensive parts of security work are the ones it hands back to you.