Differential Review
Performs security-focused differential review of code changes.
Install
npx skills add trailofbits/skills --skill differential-review -g -a claude-code -y- Repository
- trailofbits/skills7.9k
- Category
- Testing
- Updated
- 7d ago
- License
- CC-BY-SA-4.0
- Context cost
- Mediumabout 1,692 tokens
- Runs scripts
- No, instructions only
What it does
Performs security-focused differential review of code changes. Adapts analysis depth to codebase size, uses git blame for context, calculates blast radius by counting callers, checks test coverage of modified code, and generates a markdown report. Use when reviewing a PR, commit, or diff for security vulnerabilities, checking whether a change re-introduces a previously fixed bug, asking what else a change could break, or finding which modified code has no test covering it.
Differential Security Review
Security-focused code review for PRs, commits, and diffs.
Core Principles
- Risk-First: Focus on auth, crypto, value transfer, external calls
- Evidence-Based: Every finding backed by git history, line numbers, attack scenarios
- Adaptive: Scale to codebase size (SMALL/MEDIUM/LARGE)
- Honest: Explicitly state coverage limits and confidence level
- Output-Driven: Always generate comprehensive markdown report file
Rationalizations (Do Not Skip)
| Rationalization | Why It's Wrong | Required Action |
|---|---|---|
| "Small PR, quick review" | Heartbleed was 2 lines | Classify by RISK, not size |
| "I know this codebase" | Familiarity breeds blind spots | Build explicit baseline context |
| "Git history takes too long" | History reveals regressions | Never skip Phase 1 |
| "Blast radius is obvious" | You'll miss transitive callers | Calculate quantitatively |
| "No tests = not my problem" | Missing tests = elevated risk rating | Flag in report, elevate severity |
| "Just a refactor, no security impact" | Refactors break invariants | Analyze as HIGH until proven LOW |
| "I'll explain verbally" | No artifact = findings lost | Always write report |
Quick Reference
Codebase Size Strategy
| Codebase Size | Strategy | Approach |
|---|---|---|
| SMALL (<20 files) | DEEP | Read all deps, full git blame |
| MEDIUM (20-200) | FOCUSED | 1-hop deps, priority files |
| LARGE (200+) | SURGICAL | Critical paths only |
Risk Level Triggers
| Risk Level | Triggers |
|---|---|
| HIGH | Auth, crypto, external calls, value transfer, validation removal |
| MEDIUM | Business logic, state changes, new public APIs |
| LOW | Comments, tests, UI, logging |
