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Fix Review

Differential analysis to verify commits address security findings without introducing bugs.

When to Use

• Reviewing fix branches against security audit reports
• Validating that remediation commits actually address findings
• Checking if specific findings (TOB-XXX format) have been fixed
• Analyzing commit ranges for bug introduction patterns
• Cross-referencing code changes with audit recommendations

When NOT to Use

• Initial security audits (use audit-context-building or differential-review)
• Code review without a specific baseline or finding set
• Greenfield development with no prior audit
• Documentation-only changes

Rationalizations (Do Not Skip)

Quick Reference

Input Requirements

Finding Status Values

Workflow

Phase 1: Input Gathering

Collect required inputs from user:

Source commit:  [hash/ref before fixes]
Target commit:  [hash/ref to analyze]
Report:         [optional: path, URL, or "none"]

If user provides multiple target commits, process each separately with the same source.

Phase 2: Report Retrieval

When a security report is provided, retrieve it based on format:

Local file (PDF, MD, JSON, HTML): Read the file directly using the Read tool. Claude processes PDFs natively.

URL: Fetch web content using the WebFetch tool.

Google Drive URL that fails: See references/report-parsing.md for Google Drive fallback logic using gdrive CLI.

Phase 3: Finding Extraction

Parse the report to extract findings:

Trail of Bits format:

• Look for "Detailed Findings" section
• Extract findings matching pattern: TOB-[A-Z]+-[0-9]+
• Capture: ID, title, severity, description, affected files

Other formats:

• Numbered findings (Finding 1, Finding 2)
• Severity-based sections (Critical, High, Medium, Low)
• JSON with findings array

See references/report-parsing.md for detailed parsing strategies.

Phase 4: Commit Analysis

For each target commit, analyze the commit range:

# Get commit list from source to target
git log <source>..<target> --oneline

# Get full diff
git diff <source>..<target>

# Get changed files
git diff <source>..<target> --name-only

For each commit in the range:

1. Examine the diff for bug introduction patterns
2. Check for security anti-patterns (see references/bug-detection.md)
3. Map changes to relevant findings

Phase 5: Finding Verification

For each finding in the report:

1. Identify relevant commits - Match by:

   • File paths mentioned in finding
   • Function/variable names in finding description
   • Commit messages referencing the finding ID

2. Verify the fix - Check that:

   • The root cause is addressed (not just symptoms)
   • The fix follows the report's recommendation
   • No new vulnerabilities are introduced

3. Assign status - Based on evidence:

   • FIXED: Clear code change addresses the finding
   • PARTIALLY_FIXED: Some aspects fixed, others remain
   • NOT_ADDRESSED: No relevant changes
   • CANNOT_DETERMINE: Need more context

4. Document evidence - For each finding:

   • Commit hash(es) that address it
   • Specific file and line changes
   • How the fix addresses the root cause

See references/finding-matching.md for detailed matching strategies.

Phase 6: Output Generation

Generate two outputs:

1. Report file (FIX_REVIEW_REPORT.md):

# Fix Review Report

**Source:** <commit>
**Target:** <commit>
**Report:** <path or "none">
**Date:** <date>

## Executive Summary

[Brief overview: X findings reviewed, Y fixed, Z concerns]

## Finding Status

| ID | Title | Severity | Status | Evidence |
|----|-------|----------|--------|----------|
| TOB-XXX-1 | Finding title | High | FIXED | abc123 |
| TOB-XXX-2 | Another finding | Medium | NOT_ADDRESSED | - |

## Bug Introduction Concerns

[Any potential bugs or regressions detected in the changes]

## Per-Commit Analysis

### Commit abc123: "Fix reentrancy in withdraw()"

**Files changed:** contracts/Vault.sol
**Findings addressed:** TOB-XXX-1
**Concerns:** None

[Detailed analysis]

## Recommendations

[Any follow-up actions needed]

2. Conversation summary:

Provide a concise summary in the conversation:

• Total findings: X
• Fixed: Y
• Not addressed: Z
• Concerns: [list any bug introduction risks]

Bug Detection

Analyze commits for security anti-patterns. Key patterns to watch:

• Access control weakening (modifiers removed)
• Validation removal (require/assert deleted)
• Error handling reduction (try/catch removed)
• External call reordering (state after call)
• Integer operation changes (SafeMath removed)
• Cryptographic weakening

See references/bug-detection.md for comprehensive detection patterns and examples.

Integration with Other Skills

differential-review: For initial security review of changes (before audit)

issue-writer: To format findings into formal audit reports

audit-context-building: For deep context when analyzing complex fixes

Tips for Effective Reviews

Do:

• Verify the actual code change, not just commit messages
• Check that fixes address root causes, not symptoms
• Look for unintended side effects in adjacent code
• Cross-reference multiple findings that may interact
• Document evidence for every status assignment

Don't:

• Trust commit messages as proof of fix
• Skip findings because they seem minor
• Assume passing tests mean correct fixes
• Ignore changes outside the "fix" scope
• Mark FIXED without clear evidence

Reference Files

For detailed guidance, consult:

• references/finding-matching.md - Strategies for matching commits to findings
• references/bug-detection.md - Comprehensive anti-pattern detection
• references/report-parsing.md - Parsing different report formats, Google Drive fallback

Weekly Installs

400

Repository

trailofbits/skills

GitHub Stars

3.9K

First Seen

Jan 19, 2026

Security Audits

Gen Agent Trust HubFailSocketPassSnykWarn

Installed on

claude-code361

opencode313

gemini-cli299

codex286

cursor281

github-copilot246