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 |
Workflow Overview
Pre-Analysis → Phase 0: Triage → Phase 1: Code Analysis → Phase 2: Test Coverage
↓ ↓ ↓ ↓
Phase 3: Blast Radius → Phase 4: Deep Context → Phase 5: Adversarial → Phase 6: Report
Decision Tree
Starting a review?
├─ Need detailed phase-by-phase methodology?
│ └─ Read: methodology.md
│ (Pre-Analysis + Phases 0-4: triage, code analysis, test coverage, blast radius)
│
├─ Analyzing HIGH RISK change?
│ └─ Read: adversarial.md
│ (Phase 5: Attacker modeling, exploit scenarios, exploitability rating)
│
├─ Writing the final report?
│ └─ Read: reporting.md
│ (Phase 6: Report structure, templates, formatting guidelines)
│
├─ Looking for specific vulnerability patterns?
│ └─ Read: patterns.md
│ (Regressions, reentrancy, access control, overflow, etc.)
│
└─ Quick triage only?
└─ Use Quick Reference above, skip detailed docs
Quality Checklist
Before delivering:
- [ ] All changed files analyzed
- [ ] Git blame on removed security code
- [ ] Blast radius calculated for HIGH risk
- [ ] Attack scenarios are concrete (not generic)
- [ ] Findings reference specific line numbers + commits
- [ ] Report file generated
- [ ] User notified with summary
Integration
audit-context-building skill:
- Pre-Analysis: Build baseline context
- Phase 4: Deep context on HIGH RISK changes
issue-writer skill:
- Transform findings into formal audit reports
- Command:
issue-writer --input DIFFERENTIAL_REVIEW_REPORT.md --format audit-report
Example Usage
Quick Triage (Small PR)
Input: 5 file PR, 2 HIGH RISK files
Strategy: Use Quick Reference
1. Classify risk level per file (2 HIGH, 3 LOW)
2. Focus on 2 HIGH files only
3. Git blame removed code
4. Generate minimal report
Time: ~30 minutes
Standard Review (Medium Codebase)
Input: 80 files, 12 HIGH RISK changes
Strategy: FOCUSED (see methodology.md)
1. Full workflow on HIGH RISK files
2. Surface scan on MEDIUM
3. Skip LOW risk files
4. Complete report with all sections
Time: ~3-4 hours
Deep Audit (Large, Critical Change)
Input: 450 files, auth system rewrite
Strategy: SURGICAL + audit-context-building
1. Baseline context with audit-context-building
2. Deep analysis on auth changes only
3. Blast radius analysis
4. Adversarial modeling
5. Comprehensive report
Time: ~6-8 hours
When NOT to Use This Skill
- Greenfield code (no baseline to compare)
- Documentation-only changes (no security impact)
- Formatting/linting (cosmetic changes)
- User explicitly requests quick summary only (they accept risk)
For these cases, use standard code review instead.
Red Flags (Stop and Investigate)
Immediate escalation triggers:
- Removed code from "security", "CVE", or "fix" commits
- Access control modifiers removed (onlyOwner, internal → external)
- Validation removed without replacement
- External calls added without checks
- High blast radius (50+ callers) + HIGH risk change
These patterns require adversarial analysis even in quick triage.
Tips for Best Results
Do:
- Start with git blame for removed code
- Calculate blast radius early to prioritize
- Generate concrete attack scenarios
- Reference specific line numbers and commits
- Be honest about coverage limitations
- Always generate the output file
Don't:
- Skip git history analysis
- Make generic findings without evidence
- Claim full analysis when time-limited
- Forget to check test coverage
- Miss high blast radius changes
- Output report only to chat (file required)
Supporting Documentation
- methodology.md - Detailed phase-by-phase workflow (Phases 0-4)
- adversarial.md - Attacker modeling and exploit scenarios (Phase 5)
- reporting.md - Report structure and formatting (Phase 6)
- patterns.md - Common vulnerability patterns reference
For first-time users: Start with methodology.md to understand the complete workflow.
For experienced users: Use this page's Quick Reference and Decision Tree to navigate directly to needed content.