mirror of
https://github.com/trailofbits/skills
synced 2026-06-21 14:12:00 +00:00
jonnydevs
c070b9b588
* fix(fp-check): use correct JSON response format in stop hooks
Prompt-type stop hooks must respond with JSON. The previous prompts
instructed Claude to return plain text ('block' or 'approve'), causing
'Stop hook error: JSON validation failed' on every session end.
Updated both Stop and SubagentStop hook prompts to respond with:
- {"decision": "block", "reason": "..."} to prevent stopping
- {} to allow stopping (omitting decision field per Claude Code docs)
Bug discovered by Claude while debugging the JSON validation error
during active use of the fp-check skill.
* fix: use documented ok/reason schema for prompt hooks, bump to 1.0.2
Per https://code.claude.com/docs/en/hooks.md (Prompt-based hooks >
Response schema), prompt hooks must respond {"ok": true} to allow or
{"ok": false, "reason": "..."} to block — not {"decision": "block"}
or {}. Also bump to 1.0.2 since main already shipped 1.0.1 without
this fix; clients only update when the version increases.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---------
Co-authored-by: Dan Guido <dan@trailofbits.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
fp-check
A Claude Code plugin that enforces systematic false positive verification when verifying suspected security bugs.
Overview
When Claude is asked to verify suspected security bugs, this plugin activates a rigorous per-bug verification process. Bugs are routed through one of two paths:
- Standard verification — a linear single-pass checklist for straightforward bugs (clear claim, single component, well-understood bug class). No task creation overhead.
- Deep verification — full task-based orchestration with parallel sub-phases for complex bugs (cross-component, race conditions, ambiguous claims, logic bugs without spec).
Both paths end with six mandatory gate reviews. Each bug receives a TRUE POSITIVE or FALSE POSITIVE verdict with documented evidence.
Installation
/plugin install fp-check
Components
Skills
| Skill | Description |
|---|---|
| fp-check | Systematic false positive verification for security bug analysis |
Agents
| Agent | Phases | Description |
|---|---|---|
| data-flow-analyzer | 1.1–1.4 | Traces data flow from source to sink, maps trust boundaries, checks API contracts and environment protections |
| exploitability-verifier | 2.1–2.4 | Proves attacker control, creates mathematical bounds proofs, assesses race condition feasibility |
| poc-builder | 4.1–4.5 | Creates pseudocode, executable, unit test, and negative PoCs |
Hooks
| Hook | Event | Purpose |
|---|---|---|
| Verification completeness | Stop | Blocks the agent from stopping until all bugs have completed all 5 phases, gate reviews, and verdicts |
| Agent output completeness | SubagentStop | Blocks agents from stopping until they produce complete structured output for their assigned phases |
Reference Files
| File | Purpose |
|---|---|
| standard-verification.md | Linear single-pass checklist for straightforward bugs |
| deep-verification.md | Full task-based orchestration with parallel sub-phases for complex bugs |
| gate-reviews.md | Six mandatory gates and verdict format |
| false-positive-patterns.md | 13-item checklist of common false positive patterns and red flags |
| evidence-templates.md | Documentation templates for verification evidence |
| bug-class-verification.md | Bug-class-specific verification requirements (memory corruption, logic bugs, race conditions, etc.) |
Triggers
The skill activates when the user asks to verify a suspected bug:
- "Is this bug real?" / "Is this a true positive?"
- "Is this a false positive?" / "Verify this finding"
- "Check if this vulnerability is exploitable"
The skill does not activate for bug hunting ("find bugs", "security analysis", "audit code").
Methodology
Each bug is routed based on complexity:
Standard Path
For bugs with a clear claim, single component, and well-understood bug class:
- Data flow — trace source to sink, check API contracts and protections
- Exploitability — prove attacker control, bounds proofs, race feasibility
- Impact — real security impact vs operational robustness
- PoC sketch — pseudocode PoC required
- Devil's advocate spot-check — 5+2 targeted questions
- Gate review — six mandatory gates
Standard verification escalates to deep at two checkpoints if complexity warrants it.
Deep Path
For bugs with ambiguous claims, cross-component paths, concurrency, or logic bugs:
- Claim analysis — restate the vulnerability claim precisely, classify the bug class
- Context extraction — execution context, caller analysis, architectural and historical context
- Phase 1: Data flow analysis — trust boundary mapping, API contracts, environment protections, cross-references
- Phase 2: Exploitability verification — attacker control, mathematical bounds proofs, race condition proof, adversarial analysis
- Phase 3: Impact assessment — real security impact vs operational robustness, primary controls vs defense-in-depth
- Phase 4: PoC creation — pseudocode with data flow diagrams, executable PoC, unit test PoC, negative PoC
- Phase 5: Devil's advocate review — 13-question challenge with LLM hallucination self-check
- Gate reviews — six mandatory gates before any verdict