security-audit-skill Skill

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---
name: security-audit
description: Security guidance and vulnerability review for codebases, APIs, services, CLI tools, libraries, and daemons. Use for security questions, focused reviews, vulnerability research, security audits, or pen tests. Run the complete workflow only for explicit codebase audit or pen-test requests, full/comprehensive/end-to-end reviews, or requested report artifacts.
---

# Security Audit

Find vulnerabilities that violate a real trust boundary, then give owners the source evidence, safe reproduction, priority, and smallest effective fix. This is a defensive, source-first workflow. A candidate without a concrete affected principal, resource, or security outcome is not a confirmed finding.

## Operating modes

This skill is guidance by default. Loading it does not authorize the complete audit workflow or file creation.

- **Guidance mode**: For security questions, focused reviews, methodology, triage, or investigation of specific findings, use only the relevant parts of this skill. Do not automatically run all six phases, create an output directory, or write audit artifacts. You may launch focused agents when useful; they return results to the current task.
- **Full audit mode**: Use the complete workflow when the user explicitly asks to audit or pen-test a codebase, asks for a full, comprehensive, or end-to-end security review, or requests report artifacts. Run all six phases and write the files defined below.

If the request could mean either mode, ask one focused question before creating files or starting the complete workflow.

## Platform terminology

This skill is agent-neutral:

- **Parent** is the agent that coordinates the run and owns shared state.
- **Task tool** is the platform's delegation or sub-agent mechanism.
- **`research` agent** is a delegated agent for focused source exploration and factual verification.
- **`general` agent** is a delegated agent for broad investigation and bounded local execution.
- **`subagent_type:`** in a heading names which of these two delegated agent roles runs that work.

Use equivalent platform capabilities while preserving role, write-isolation, prompt, and independence boundaries.

## Universal execution safety

These rules apply in both operating modes. Source inspection is read-only. Run target-controlled builds, tests, processes, browsers, emulators, fuzzers, and fixture processing only inside an OS-enforced sandbox that provides all of these controls:

- no external network; use only an isolated loopback namespace when the check needs local client/server traffic;
- an empty environment populated from an explicit allowlist with safe values, with scratch-local `HOME`, temporary directories, and caches;
- a read-only target and toolchain, with the target-controlled process able to write only inside its assigned `scratch/` directory; and
- explicit low CPU, memory, process, file-size, disk, and wall-clock limits.

The agent, outside the target-controlled process, may make a disposable source copy in an assigned `scratch/` directory when a build must write beside source. In guidance mode, do not retain target-controlled files. In full audit mode, only trusted parent-side code may promote the minimum non-secret result to retained `artifacts/` using the procedure under Write isolation. Never expose a retained output directory (other than the agent's own assigned `scratch/`), another agent's directory, the host home directory, credentials, sockets, or shared services to target code. Do not install dependencies or let builds fetch them. Use only tools and dependencies already available locally. If every control cannot be enforced, do not execute target code: report the missing sandbox capability as a needs-validation blocker and give a safe validation plan.

Use dummy principals, fixtures, and secrets. Do not probe deployed endpoints, external services, shared infrastructure, production identities, other users' data, or live control planes. Do not test availability against a live or shared process, publish artifacts, alter releases, spend paid API quota, or continue beyond the minimum local effect needed to establish a defect. If the decisive fact is outside source or the sandboxed fixture, report it as needing validation.

## Full audit setup

In full audit mode, resolve these values before reconnaissance:

- **Skill directory**: the absolute directory containing this `SKILL.md`.
- **Target**: the absolute repository root under review.
- **Repo name**: a stable repository identifier from the directory or local Git remote.
- **Output directory**: a new writable directory outside the target, defaulting to `~/security-audit-skill/<repo-name>/run-<N>`, where `<N>` is the next unused integer. Use a directory inside the target only when the user explicitly selects it and the parent verifies that version control ignores the whole directory. Otherwise stop and request an external path.
- **Source ref**: the reviewed commit and whether the worktree is dirty. Do not treat unreviewed generated or modified files as another revision.

### Write isolation

The parent creates and is the only writer of shared run files:

- `run-metadata.json`
- `architecture.md`
- `coverage-ledger.json`
- `findings.json`
- `REPORT.md`
- `FINDINGS-DETAIL.md`
- `NEEDS-VALIDATION.md`

Each hunter or verifier receives a unique root under `<output-dir>/agents/<agent-id>/`, with separate `scratch/` and `artifacts/` directories. Canonical agent IDs match `^[a-z0-9][a-z0-9_-]{0,63}$` and must not equal a Windows device name such as `con`, `prn`, `aux`, `nul`, `com1` through `com9`, or `lpt1` through `lpt9`. Lowercase IDs prevent case-fold collisions. The agent and every target-controlled process may write only to `scratch/`; retained `artifacts/` is parent-owned, is never exposed to the sandbox, and is writable only by trusted parent-side promotion code. Agents may not change shared files, target source, retained artifacts, or another agent's directory. Do not use `/tmp` or the host home directory as a writable fallback.

Before execution, the parent opens and retains trusted, non-inheritable directory descriptors for the agent's `scratch/` and `artifacts/` roots, and records an allowlist of expected scratch-relative artifact files plus explicit per-file and cumulative byte limits. Never pass those descriptors to the agent or sandbox. After the sandbox and all its processes terminate, trusted parent-side code promotes each allowlisted file separately:

1. Validate the declared relative path: reject absolute, empty, `.`, `..`, or symlinked components.
2. Walk each parent component from the retained scratch-root descriptor with no-follow directory-relative operations; never reopen by path.
3. Open the leaf no-follow and nonblocking.
4. Verify with `fstat` that it is a regular file with link count exactly one and within the recorded per-file and cumulative byte limits.
5. Enforce those limits again while reading from that descriptor.
6. Copy exactly the verified size, repeat `fstat`, and reject a changed identity, type, link count, or size.
7. For the destination, walk every parent component from the retained artifacts-root descriptor with no-follow directory-relative operations; require each existing component to be a real directory, and create any missing directory exclusively before reopening and verifying it no-follow.
8. Create the leaf exclusively without following links, verify that the opened destination is a regular file with link count exactly one, and copy from the verified source descriptor without reopening either path.
9. Use equivalent race-safe APIs on non-POSIX systems.
10. Never recursively copy or glob scratch, extract an archive into artifacts, or open or promote a symlink, FIFO, socket, device, directory, hard-linked file, changing file, or file that exceeds its bound.
11. If any check is unavailable, cannot be enforced, or fails, discard the scratch entry; if it is decisive evidence, retain `needs_v