# Review by Staff Security Engineer (Round 1)

## Review Complete — Staff Security Engineer

**VERDICT: approve**

### Key Findings

**Security posture is solid.** The implementation correctly applies double-sanitization (`sanitize_untrusted_content()` → `sanitize_for_slack()`) at all 7 points where untrusted content enters the Slack formatting pipeline. This prevents:
- **Slack mrkdwn injection** (`*`, `_`, `~`, `` ` `` escaped)
- **Mention injection** (`@here`, `@channel`, `@everyone` neutralized to `[mention]`)
- **Link phishing** (`<url|text>` patterns decomposed)
- **Blockquote injection** (leading `>` neutralized with zero-width space)
- **Information leakage** (3,000-char truncation at all 4 `slack_note()` call sites)

**Two low-severity gaps for follow-up (non-blocking):**
1. **Non-HTTP link schemes** — `_SLACK_LINK_INJECTION_RE` only catches `http`/`https` links. `mailto:` and `slack://` link patterns could slip through. Mitigated by the XML sanitizer stripping angle-bracket tags upstream.
2. **User mention injection** — `<@U12345>` patterns aren't covered by the mention regex. Requires a valid Slack user ID and surviving the XML sanitizer, making exploitation unlikely.

**121 tests pass**, including dedicated sanitization integration tests that verify the escape chain flows through all formatting functions end-to-end. All PRD requirements (FR-1 through FR-5) are implemented, all tasks complete, no TODOs or placeholder code.

Review artifact saved to `cOS_reviews/reviews/staff_security_engineer/20260331_192000_round1_when_you_output_followups_in_the_thread_on_slack_a938599349.md`.
