# Review by Staff Security Engineer (Round 5)

## Staff Security Engineer — Round 5 Review Complete

**137 tests pass.** All 5 functional requirements implemented across 10 commits (+1,371 / -24 lines).

### Security Assessment

The sanitization architecture is sound and correctly layered:
1. **`sanitize_untrusted_content()`** strips XML tags (inner layer)
2. **`sanitize_for_slack()`** escapes mrkdwn, neutralizes mentions/links/blockquotes (outer layer)

Applied consistently at all 7 ingress points where untrusted content enters Slack messages. Ordering is correct — XML stripping before Slack escaping prevents cross-layer bypass.

All major Slack injection vectors covered: `@here`/`@channel`/`@everyone` mention spam, `<!here>` special mentions, `<@U12345>` user mentions, `<url|phishing>` link injection, mrkdwn formatting injection, and blockquote injection. Bare link regex correctly expanded to arbitrary URI schemes.

Truncation (72 chars/field, 3000 chars/message) provides defense-in-depth against information leakage. Audit logging enables investigation.

**Non-blocking findings:** (1) Findings parser lines are sanitized post-extraction — safe. (2) Zero-width space blockquote neutralization is standard but invisible.

VERDICT: **approve**

Review artifact saved to `cOS_reviews/reviews/staff_security_engineer/20260331_210000_round5_when_you_output_followups_in_the_thread_on_slack_a938599349.md`.
