Security Scan Skill for Claude

Security scan — orchestrate scanners, triage the noise, emit a gate

A machine-first vulnerability sweep. Point automated scanners at a codebase,

collect SARIF/JSON, then do the work that has actual value: dedupe cross-tool

overlap, rank by exploitability, and emit one gate artifact CI can act on. The

finding comes from a tool run, not a hunch — if you are reasoning about a

design or hand-writing a fix, that is secure-coding,

not this skill.

Your job is orchestration + triage: every finding traces to a scanner run with a

ruleId and a source location, so the output is reproducible. Not eyeballing

code, not authoring patches.

Read-only by default. Scan, triage, report. Apply fixes (version bumps,

rotation, .gitignore edits) only when the user asks — a security sweep that

silently mutates the tree destroys the evidence and the trust.

Pin and verify your scanners. Exact versions, verified checksums/SHAs, never

@latest GitHub Actions. In March 2026 Trivy was supply-chain compromised —

malicious releases v0.69.4/0.69.5/0.69.6 and a hijacked

aquasecurity/trivy-action exfiltrated CI secrets. Your scanner runs with repo +

CI-secret access; an unpinned scanner is itself the attack surface.

Scan classes and tool selection

Four classes: SAST (injection, XSS, path traversal in *first-party* code),

SCA / deps (known CVEs in dependency manifests + lockfiles), Secrets

(credentials in the tree or git history), Misconfig / IaC (Dockerfile,

k8s, Terraform, exposed config). Pick tools by what is in the repo. This is the

real branch point — match the tool to the manifest, do not run everything

everywhere.

| Repo contains | SAST | SCA | Secrets | Misconfig |

|---|---|---|---|---|

| Node (package-lock.json/pnpm-lock.yaml) | Semgrep | osv-scanner + npm audit (fast) | gitleaks → TruffleHog | Trivy |

| Python (poetry.lock/requirements.txt) | Semgrep | osv-scanner + pip-audit (fast) | gitleaks → TruffleHog | Trivy |

| Go (go.mod/go.sum) | Semgrep | osv-scanner (+ govulncheck for reachability) | gitleaks | Trivy |

| Containers (Dockerfile, images) | — | Trivy fs/image | Trivy --scanners secret | Trivy config |

| IaC (Terraform/k8s/Helm) | Semgrep (IaC rules) | — | gitleaks | Trivy config, Semgrep rulesets |

| Monorepo (mixed) | Semgrep auto | osv-scanner (multi-ecosystem) | gitleaks → TruffleHog | Trivy |

Full install (pinned), flag matrix, and suppression syntax: references/tools.md.

Run recipes

All recipes emit SARIF (or JSON you normalize to it) — a common schema is what

lets you merge four tools, dedupe, and feed one artifact into CI instead of four

incompatible logs. Pin the version shown; the placeholders below mark where

to lock an exact tag/digest.

SAST — Semgrep

Free OSS edition (latest 1.164.0, 2026-05-27): 30+ languages, ~2,000 community

rules. SCA + Secrets rulesets are gated behind the hosted platform — use the

dedicated tools below for those, not Semgrep.

# Pin via the CLI version, not @latest. OWASP ruleset, SARIF out.
semgrep scan --config p/owasp-top-ten --sarif --output sast.sarif .
# Broader local sweep (community rules), no telemetry:
semgrep scan --config auto --sarif --output sast.sarif --metrics off .

SCA — osv-scanner (primary), native auditors (fast pass)

osv-scanner (OpenSSF/Google) checks lockfiles against OSV.dev across ecosystems

and catches transitive CVEs the native auditors miss. Run native first for

speed, osv-scanner for coverage — never native alone.

# Primary: lockfile-aware, multi-ecosystem, SARIF.
osv-scanner scan source --format sarif --output sca.sarif .
# Fast first pass (ecosystem-native, weaker on transitive):
npm audit --omit=dev --audit-level=high --json > npm-audit.json   # Node
pip-audit --format json --output pip-audit.json                   # Python

Secrets — gitleaks (tree + history), TruffleHog (verified)

gitleaks (~150+ patterns, sub-second on diffs) is the pre-commit/CI workhorse.

TruffleHog (800+ types) adds live credential verification — it auth-tests a

hit to tell a real leaked key from a sample. Scan history, not just the tree:

a key deleted in HEAD is still in the pack files and still rotatable.

# gitleaks: redacted SARIF over the working tree AND full git history.
gitleaks detect --redact --report-format sarif --report-path secrets.sarif
# TruffleHog: only verified (live) secrets across history.
trufflehog git file://. --only-verified --json > trufflehog.json

Misconfig / IaC — Trivy (PINNED — see the caveat above)

Trivy scans filesystems, images, and IaC and finds transitive CVEs npm audit

misses.

# Pin the EXACT version (NOT v0.69.4/.5/.6 — those were the malicious releases).
# Verify the checksum/cosign signature before first use. See references/tools.md.
trivy fs --scanners vuln,secret,misconfig --format sarif --output trivy.sarif .

Triage — turn noise into a ranked report

The deliverable is not the four SARIF files. It is a deduped, ranked report.

• Merge + dedupe. Cross-tool overlap is real (osv-scanner and Trivy both

flag the same CVE; gitleaks and TruffleHog both flag the same key). Key on

(class, normalized-id, path, line) and keep the richest record — prefer the

one with verification (TruffleHog) or reachability (govulncheck).

• Normalize severity. SARIF level and tool-native severities disagree;

map them all to one critical/high/medium/low scale (references/triage.md).

• Rank by exploitability, not by count. A finding scores higher when it is

reachable (called, not just present) + exposed (on an untrusted path)

+ a sensitive sink (auth, money, PII, RCE). A verified live secret or a

reachable RCE CVE outranks a theoretical lib finding behind a feature flag.

• Suppress with a written justification, never a blanket ignore. Each

suppression records *who, why, and an expiry* — not a silent .semgrepignore

that hides the next real bug too.

BAD  — dump 412 raw findings from four tools, sorted alphabetically, no ranking.
GOOD — 3 unsuppressed criticals first:
       1. [secrets] VERIFIED live Stripe sk_live_… in config/.env (history) → ROTATE NOW
       2. [sca] CVE-2024-… lodash 4.17.20 transitive, reachable in src/api/parse.ts → bump 4.17.21
       3. [sast] SQL built from req.query in routes/search.js:48 → parameterize
       + 7 mediums summarized, + 18 suppressed (each with justification + expiry).

Full ranking rubric, dedupe keying, and severity-normalization map:

references/triage.md.

The gate artifact

Emit one security-scan-report.json — the machine-checkable contract CI gates on.

{
  "schemaVersion": "1.0",
  "scannedAt": "2026-06-02T10:00:00Z",
  "target": ".",
  "tools": [{ "name": "osv-scanner", "version": "2.0.2" }],
  "summary": { "critical": 1, "high": 2, "medium": 7, "low": 14, "suppressed": 18 },
  "findings": [
    {
      "class": "sca",
      "ruleId": "CVE-2024-XXXXX",
      "path": "package-lock.json",
      "line": 0,
      "severity": "critical",
      "status": "open",
      "tool": "osv-scanner",
      "exploitability": "reachable",
      "title": "Prototype pollution in lodash <4.17.21"
    }
  ]
}

• status is one of open | suppressed | fixed; severity one of

critical | high | medium | low. Schema in full: references/triage.md.

• Gate rule: any open finding at critical (and, on a strict gate, high)

→ fail. suppressed never fails. scripts/verify.sh enforces exactly this and

exits 0 on a clean/empty report (no false failure).

CI wiring (brief)

• Pin actions to a full commit SHA, not a tag, never @latest — the hijacked

aquasecurity/trivy-action was pulled by tag.

# .github/workflows/security-scan.yml — pin the SHA, verify before bumping.
- uses: aquasecurity/trivy-action@<full-40-char-sha>  # NEVER @latest / @master
  with: { scan-type: fs, format: sarif, output: trivy.sarif }
- run: ./scripts/verify.sh   # gate on security-scan-report.json

• Upload SARIF to code scanning; gate the merge on verify.sh, not on a human

reading logs. See github-actions for the

pipeline shell and verify for the broader green gate

this feeds.

Anti-patterns

| Anti-pattern | Do instead |

|---|---|

| Pulling aquasecurity/trivy-action@latest because it is the official action | March 2026: a hijacked tag stole CI secrets. Pin a full SHA, verify provenance. |

| Treating every scanner finding as a bug to fix | Most are noise. Rank by reachable + exposed + sensitive sink; report the few that matter. |

| Calling the repo clean after scanning only the working tree | History holds the deleted keys. Scan git history; a removed-in-HEAD key is still leaked and live. |

| Declaring deps fine because npm audit is clean | Native auditors miss transitive CVEs. Run osv-scanner/Trivy too; native is the fast pass, not the only pass. |

| Committing a blanket .semgrepignore to quiet CI | A blanket ignore hides the next real bug. Suppress per-finding with a written justification + expiry. |

| Deleting a verified key from the file and moving on | Deleting ≠ safe. Rotate the credential first, then scrub history. The committed value is already compromised. |

| Taking the SARIF level as the severity | Tools disagree. Normalize to one scale before you rank or gate. |

| Dumping all four tool outputs in the PR for the reviewer to sort | The reviewer won't. Merge, dedupe, rank, and emit one report. |

| Letting the scan auto-fix the deps it finds | Read-only by default. Propose bumps; apply only when asked — never mutate during a sweep. |

Project grounding (02-DOCS + CLAUDE.md)

In a project with a 02-DOCS/ layer (the harness

Karpathy wiki), record the scanner choices, pinned versions, gate thresholds, and

any accepted-risk suppressions in 02-DOCS/wiki/stack/security-scan.md, and index

it in 02-DOCS/wiki/index.md (the Knowledge map; root CLAUDE.md keeps only a short

pointer to it). Read it first on every run so the next agent inherits the pinned

tools and thresholds instead of re-deriving them. No 02-DOCS/? Skip silently.

Conventions are recorded, not gated — never block the scan on this.

See Also

Reviewing a diff rather than scanning a repo: code-review

for correctness and quality, review for adversarial review

against a spec.