Testing CORS Misconfiguration

When to Use

• During authorized penetration tests when assessing API endpoints for cross-origin access controls
• When testing single-page applications that make cross-origin API requests
• For evaluating whether sensitive data can be exfiltrated from a victim's browser session
• When assessing microservice architectures with multiple domains sharing data
• During security audits of applications using CORS headers for cross-domain communication

Prerequisites

• Authorization: Written penetration testing agreement for the target
• Burp Suite Professional: For intercepting and modifying Origin headers
• Browser with DevTools: For observing CORS behavior in real browser context
• Attacker web server: For hosting CORS exploitation PoC pages
• curl: For manual CORS header testing
• Python HTTP server: For hosting exploit pages locally

Workflow

Step 1: Identify CORS Configuration on Target Endpoints

Check all API endpoints for CORS response headers.

# Test with a foreign Origin header
curl -s -I \
  -H "Origin: https://evil.example.com" \
  "https://api.target.example.com/api/user/profile"

# Check for CO…