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ISSUE_262_XSS_SANITIZATION.md

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Issue #262: Input Sanitization for XSS Prevention

Summary

Added input sanitization middleware to prevent stored XSS attacks in user-provided content, specifically the reason field in verification reports.

Changes Made

1. Created Sanitizer Module

  • File: backend/src/sanitizer.ts
  • Purpose: XSS prevention via:
    • Stripping HTML tags (script, iframe, etc.)
    • Encoding HTML entities
    • Removing event handlers (onerror=, onclick=, etc.)

2. Database Schema Update

  • File: backend/src/database.ts
  • Changes:
    • Added asset_reports table to store individual reports with reason for audit trail
    • Added saveAssetReport() function to persist sanitized reasons

3. API Endpoint Update

  • File: backend/src/api.ts
  • Endpoint: POST /api/verification/report
  • Changes:
    • Imported sanitizeInput from sanitizer module
    • Imported saveAssetReport from database
    • Added sanitization of reason field before storing
    • Stores sanitized reason in asset_reports table

4. Unit Tests

  • File: backend/src/__tests__/sanitizer.test.ts
  • Coverage: 11 test cases covering:
    • Null/undefined handling
    • Script tag removal
    • Iframe tag removal
    • HTML entity encoding
    • Event handler removal
    • Safe content preservation

Security Considerations

What This Prevents

  • Stored XSS attacks via reason field in verification reports
  • Script injection through HTML tags
  • Event handler exploitation (onerror, onclick, etc.)
  • JavaScript URL injection

Attack Vectors Mitigated

# Before (vulnerable):
POST /api/verification/report
{ "assetCode": "USDC", "issuer": "...", "reason": "<script>alert(1)</script>" }

# After (sanitized):
POST /api/verification/report
{ "assetCode": "USDC", "issuer": "...", "reason": "alert1" }

Testing

# Run tests
cd backend
npm test

# Test specific module
npx vitest run sanitizer

Checklist

  • Create sanitizer module with XSS protection
  • Update database schema with asset_reports table
  • Add saveAssetReport database function
  • Integrate sanitization in verification report endpoint
  • Add unit tests for sanitizer
  • Verify no TypeScript errors

Related Issues

  • Issue #260: HMAC Signature Verification for Webhooks
  • Issue #261: Contract Upgrade Authorization with Timelock