🔥 4-Step API Testing Methodology

Advanced API Vulnerability Discovery Use Case: Bug Bounty & API Security Testing

1️⃣ Find Sensitive API Endpoints

Target endpoints that commonly leak sensitive data:

  • User PII (emails, phone numbers, addresses)
  • Financial data (transactions, balances)
  • Authentication tokens & session data
  • Internal system information
  • Admin-level data in user endpoints

Common sensitive endpoints

/api/v1/users/[ID]
/api/admin/config
/api/internal/metrics
/api/orders/[ID]
/api/transactions
/api/profile/private

2️⃣ Cache Headers Analysis

Check response headers for caching indicators:

  • Cache-Control: public, max-age=3600 ← CACHED
  • CF-Cache-Status: HIT ← Cloudflare cached
  • X-Cache: HIT ← Generic cache hit
  • Age: 300 ← 5 minutes in cache
  • ETag: "abc123" ← Entity tag for cache validation
  • Via: 1.1 varnish ← Proxy caching

If cached → try Web Cache Deception:

Legitimate: /api/users/me/profile
Deception:  /api/users/me/profile.css
Deception:  /api/users/me/profile/

3️⃣ HTTP Method Changing

Bypass auth/validation with method switching. Examples:

GET /api/admin/users → 403 Forbidden
POST /api/admin/users → 200 OK + user list
GET /api/config → 404 Not Found
HEAD /api/config → 200 OK
POST /api/search → 403 Forbidden
PUT /api/search → 200 OK + results

4️⃣ Array-Based IDOR Testing

When you find /api/users/123 test these array/IDOR patterns:

/api/users/[123,124]
/api/users/123,124
/api/users/123&124
/api/users/?id[]=123&id[]=124
/api/users/?ids=123,124
/api/users/?user_ids=123,124
/api/batch/users?ids=123,124

🎯 Real-World Attack Chain (Example)

  1. Discover endpoint /api/v1/users/456
  2. Check headers → X-Cache: HIT, max-age=300
  3. Change GET to POST → bypass rate limiting
  4. Test array IDOR → /api/v1/users/[456,457,458] Result: Mass user data leakage + cached responses

🛡 Defense Recommendations

  • Consistent Authorization — Apply same checks across all HTTP methods
  • Input Validation — Reject array parameters unless explicitly allowed
  • Cache Control — Use Cache-Control: private for sensitive data
  • API Schema Enforcement — Validate against OpenAPI specification
  • Audit Logging — Monitor for unusual parameter patterns

💡 Pro Testing Tips

  • Use Burp's "Change Request Method" extension
  • Automate with tools like katana or ffuf for endpoint discovery
  • Always test both authenticated and unauthenticated contexts
  • Combine techniques (cache analysis + method change + IDOR) for maximum impact

🔔 Follow @cybersecplayground for advanced API hacking techniques! Like & Share if you found your first IDOR with this! 💰

#APISecurity #BugBounty #IDOR #WebCacheDeception #CyberSecurity #APITesting #Hacking #SecurityResearch