# Staff Security Engineer — Round 5 Review

**Branch:** `colonyos/when_you_output_followups_in_the_thread_on_slack_a938599349`
**PRD:** `cOS_prds/20260331_190640_prd_you_are_a_code_assistant_working_on_behalf_of_the_engineering_team_the_following.md`
**Tests:** 137 pass (test_sanitize.py + test_slack_formatting.py)
**Commits:** 10 commits, +1,371 / -24 lines

## Checklist

### Completeness
- [x] FR-1: Task completion messages include description (truncated, sanitized)
- [x] FR-2: Task outline uses bullet formatting with `•` and `+N more` overflow
- [x] FR-3: Task result summary includes descriptions with cost/duration
- [x] FR-4: Review round messages include condensed finding summaries
- [x] FR-5: All user-derived content sanitized (dual-layer: XML strip + Slack mrkdwn escape)
- [x] All tasks marked complete across 10 commits
- [x] No placeholder or TODO code remains

### Quality
- [x] 137 tests pass
- [x] Code follows existing project conventions (private helpers, named constants)
- [x] No unnecessary dependencies added
- [x] No unrelated changes included

### Safety
- [x] No secrets or credentials in committed code
- [x] No destructive database operations
- [x] Error handling present (ValueError/TypeError on cost/duration with debug logging)

## Security-Specific Assessment

### Sanitization Architecture (FR-5) — Sound

The dual-layer sanitization is correctly ordered at all 7 ingress points:

1. `sanitize_untrusted_content()` — strips XML-like tags (prevents prompt/markup injection from LLM outputs echoing user content)
2. `sanitize_for_slack()` — escapes mrkdwn metacharacters, neutralizes mention injection (`@here`/`@channel`/`<!everyone>` → `[mention]`), defuses link injection (`<url|text>` → `url - text`), neutralizes blockquote (`>`) with zero-width space

**Ordering is correct:** XML stripping happens first (inner), then Slack escaping (outer). This prevents an attacker from crafting content where the Slack-escaping step inadvertently creates valid XML tags.

### Injection Vectors Covered

| Vector | Mitigation | Test Coverage |
|--------|-----------|---------------|
| `@here`/`@channel`/`@everyone` mention spam | Replaced with `[mention]` | ✅ 3 tests |
| `<!here>`/`<!channel>`/`<!everyone>` Slack special mentions | Replaced with `[mention]` | ✅ 3 tests |
| `<@U12345>` user mention injection | Replaced with `[mention]` | ✅ 1 test |
| `<url\|phishing text>` link injection | Decomposed to `url - text` | ✅ 2 tests |
| `*bold*`/`_italic_`/`` `code` ``/`~strike~` formatting injection | Backslash-escaped | ✅ 4 tests |
| `> blockquote` injection | Zero-width space prefix | ✅ 1 test |
| XML tag injection from LLM output | Stripped by `sanitize_untrusted_content()` | ✅ existing tests |

### Bare Link Regex Improvement

The `_SLACK_BARE_LINK_RE` regex was expanded from `https?://` to `[a-zA-Z][a-zA-Z0-9+.-]*://` — correctly covers arbitrary URI schemes (e.g., `slack://`, `file://`, `ftp://`) that could be used for protocol-handler exploitation. Good fix.

### Truncation as Defense-in-Depth

- Per-field: task descriptions capped at 72 chars, findings at 80 chars
- Per-message: 3,000 char hard cap via `_truncate_slack_message()`
- This limits information leakage if review findings accidentally echo secrets or internal paths from source code — even if sanitization misses something, truncation bounds the exposure

### Audit Logging

`sanitize_for_slack()` emits `logger.debug()` when content is modified, and the `_format_task_list_with_descriptions` cost/duration parser logs malformed values. This provides an audit trail for investigating unexpected content neutralization.

### Remaining Observations (Non-blocking)

1. **[src/colonyos/orchestrator.py]**: The `_extract_review_findings_summary` parser's `stripped.startswith("- ")` check could theoretically match a line like `- ` followed by attacker-controlled content, but since the content is subsequently passed through `sanitize_for_slack(sanitize_untrusted_content(...))`, this is safe.

2. **[src/colonyos/sanitize.py]**: The zero-width space (`\u200b`) blockquote neutralization is invisible to users. If Slack ever changes how it renders zero-width spaces, this could silently break. Low risk — standard approach used by other Slack bots.

---

VERDICT: approve

FINDINGS:
- [src/colonyos/orchestrator.py]: `_extract_review_findings_summary` finding lines pass through dual-layer sanitization — safe even if attacker controls review output format
- [src/colonyos/sanitize.py]: Zero-width space blockquote neutralization is invisible to users; standard but worth noting for future maintenance

SYNTHESIS:
This implementation is production-ready from a security perspective. The sanitization architecture is well-designed with correct ordering (XML strip → Slack escape) applied consistently at all ingress points. The seven primary injection vectors for Slack mrkdwn are mitigated with comprehensive test coverage (137 tests). Truncation provides defense-in-depth against information leakage. Audit logging enables investigation of content neutralization events. The two non-blocking findings from round 4 (debug logging for malformed cost/duration, tighter blank-line handling in findings collection) have been addressed. No remaining security concerns warrant blocking. Ship it.
