caro-security-update

name	caro.security.update
description	Maintainer skill to draft a CVE rule YAML via Nimble for a specific CVE, fill pattern + test_cases, and open a PR. Used off-cycle when a 0day lands between weekly cron runs.

caro.security.update Skill

Purpose: Manually trigger the Nimble CVE authoring pipeline for a single CVE (or a batch) outside the weekly cron window. Use this when a high-severity 0day is disclosed and protection shouldn't wait until Monday 09:00 UTC.

Spec: specs/010-nimble-cve-pipeline/ Companion workflow: .github/workflows/cve-rule-sync.yml Orchestrator script: scripts/nimble-cve-sync.ts

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When to Use

• A CVE or 0day lands with CVSS ≥ 7.0 and a plausible shell-invocation vector
• The weekly cron won't run for > 24h and the exposure window matters
• You want to re-author an existing rule after the advisory was amended
• You are reviewing an auto-drafted PR and want to fill the TODO_NIMBLE_AUTHORED placeholder without leaving the CLI

Do not use for:

• Non-shell CVEs (daemons, kernels, libraries without a shell attack surface)
• User-local custom rules — that's Dogma tier-3 (~/.caro/rules/)
• Generic pattern additions not tied to a CVE — use safety-pattern-developer instead

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Prerequisites

• Maintainer access to wildcard/caro
• Working gh CLI auth
• scripts/node_modules/ installed (cd scripts && npm ci)
• Nimble access: either NIMBLE_API_KEY in env for nimble CLI, OR the nimble-agents MCP server available in the Claude session
• Optional: NVD_API_KEY env var to raise NVD rate limit

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Workflow

Phase 1 — Identify the CVE (2 min)

Confirm the CVE ID and authoritative source. Default to the NVD detail page: https://nvd.nist.gov/vuln/detail/CVE-YYYY-NNNNN. If the CVE isn't in NVD yet (freshly-assigned MITRE IDs can lag 24-48h), use the upstream advisory.

Capture:

• CVE ID (format CVE-YYYY-NNNNN)
• Advisory URL (NVD preferred; GHSA / vendor page acceptable)
• Disclosure date (ISO YYYY-MM-DD)
• CVSS base score
• Affected shell tool(s) — if none, stop here; this skill is out of scope.

Phase 2 — Fetch + draft (1 min)

From repo root on a fresh feature branch:

bin/sk-new-feature "security cve <cve-id>"
cd .worktrees/NNN-security-cve-<cve-id>

# Fetch the specific CVE window from NVD + KEV + GHSA.
# Use a 2-day window centered on disclosure for max recall.
npx -w scripts tsx scripts/nimble-cve-sync.ts \
  --since $(date -d '<disclosed> - 1 day' +%Y-%m-%d) \
  --max 5

Check that data/cve_rules/CVE-YYYY-NNNNN.yaml exists. If the sync didn't produce it (CVE not yet in any feed), hand-draft the skeleton:

cp data/cve_rules/EXAMPLE-TEMPLATE.yaml data/cve_rules/CVE-YYYY-NNNNN.yaml
$EDITOR data/cve_rules/CVE-YYYY-NNNNN.yaml

Phase 3 — Author the pattern via Nimble (5-15 min)

The draft YAML has pattern: TODO_NIMBLE_AUTHORED and test_cases: []. These are the model-authored parts. Two paths:

Path A — Nimble MCP (preferred inside Claude Code):

Ask Claude with the nimble-agents MCP available:

Use nimble_extract on the CVE advisory URL, then nimble_agents_run with the cve-pattern-author agent (or nimble_search for advisories that need synthesis) to propose:

1. A regex pattern that matches exploit invocations without false-positiving on benign shell usage
2. At least 2 test_cases with expected_behavior: Block that exercise the exploit trigger
3. At least 2 test_cases with expected_behavior: Allow that exercise nearby benign commands

Write the result directly into data/cve_rules/CVE-YYYY-NNNNN.yaml.

Path B — Nimble CLI (scripting / CI):

nimble extract "https://nvd.nist.gov/vuln/detail/CVE-YYYY-NNNNN" \
  --focus academic \
  > /tmp/cve-context.md
# Feed /tmp/cve-context.md to your pattern-generation prompt, then
# edit the YAML file with the proposed pattern + test_cases.

Phase 4 — Validate (30 sec)

npx -w scripts tsx scripts/validate-cve-yaml.ts \
  data/cve_rules/CVE-YYYY-NNNNN.yaml

Must exit 0. Common failures:

Error	Fix
risk_level — must be one of [safe, moderate, high, critical]	Lowercase only
test_cases — must contain at least one expected_behavior: Allow case	Add a benign command that must NOT be blocked
id — must match filename stem	Filename and YAML id: must agree
pattern — not a valid regex	Escape ., $, `

Phase 5 — Local smoke test (1 min)

Build with the new rule and confirm it blocks the exploit:

cargo build --release --features cve-rules
./target/release/caro --version | grep 'CVE rules:'

# Replace with a Block test case from your YAML:
./target/release/caro --dry-run "<exploit invocation>"
# Expect: ✗ BLOCKED with the CVE ID in the reason string.

# And a benign Allow test case:
./target/release/caro --dry-run "<benign invocation>"
# Expect: ✓ allowed (not blocked by the new rule).

Phase 6 — Open PR (2 min)

git add data/cve_rules/CVE-YYYY-NNNNN.yaml
git commit -m "feat(cve-rules): add CVE-YYYY-NNNNN pattern

Adds pattern for <one-line CVE summary>. CVSS <score>.
Source: <advisory URL>.

Co-Authored-By: Claude Sonnet 4.6 <[e-mail]>"
git push -u origin HEAD

gh pr create \
  --title "feat(cve-rules): add CVE-YYYY-NNNNN pattern" \
  --label "cve-rules" \
  --label "security" \
  --body "..."

PR body must include:

• CVE ID + source URL
• CVSS score
• Why this can't wait for weekly cron (if using this skill for urgency)
• The pattern and a one-line rationale for regex shape
• Block + Allow test cases with expected behaviors
• Sign-off checklist from data/cve_rules/README.md

Phase 7 — Request review

Maintainer review required before merge. No auto-merge, even at CVSS ≥ 9 — a false-positive pattern blocks all users until the next release.

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Troubleshooting

Problem	Likely cause	Resolution
Sync returns 0 candidates for a known CVE	Feed propagation lag (NVD can be 24-48h behind MITRE)	Hand-draft from template
Pattern matches benign commands in ad-hoc testing	Too broad	Tighten the regex; add the benign command to test_cases with Allow and re-test
cargo build fails with CVE_COMPILED deserialize error	Stale $OUT_DIR/cve_patterns.bin	cargo clean -p caro && cargo build
--version doesn't show new count	Feature flag off	Build with --features cve-rules (default-on)
Validator passes but cargo test safety regresses	Pattern collides with a static rule	Dedup in src/dogma/compiler.rs should handle this — file an issue if not

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Non-negotiables

• Every PR is human-reviewed. No auto-merge.
• Every rule ships with tests. No exceptions.
• Every rule has a source URL. Unsourced patterns are rejected at review.
• Lowercase risk_level. Serde is strict.
• Pattern regex must compile. Validator catches this; don't ship broken regex.

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Related

• safety-pattern-developer — TDD skill for non-CVE pattern additions
• safety-pattern-auditor — audits the full ruleset for gaps
• .github/workflows/cve-rule-sync.yml — weekly cron equivalent
• data/cve_rules/README.md — reviewer checklist + pattern guidelines