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After discovering API documentation, always test all endpoints—some may accept your JWT token and grant unintended access, leading to unauthorized data exposure or financial loss.
You Should Know:
1. Testing JWT Vulnerabilities
Use tools like Burp Suite or Postman to replay requests with your JWT token. Check for:
– Insecure Direct Object References (IDOR)
– Privilege Escalation
– Token Replay Attacks
2. Common JWT Exploits
- None Algorithm Bypass: Modify the JWT header to use
"alg": "none".eyJhbGciOiJub25lIn0.eyJ1c2VyIjoiYWRtaW4ifQ. Example tampered JWT
- Weak Secret Cracking: Use `hashcat` to brute-force weak JWT secrets.
hashcat -m 16500 jwt.txt rockyou.txt
- Kid Injection: Manipulate the `kid` (Key ID) parameter to point to a malicious key.
3. Automated Scanning with `jwt_tool`
python3 jwt_tool.py <JWT_TOKEN> -T
This tests for common vulnerabilities, including:
- Signature bypass
- Header injection
- Algorithm confusion
4. Mitigation Steps
- Always validate JWT signatures on the server.
- Use strong secrets (e.g., 256-bit HMAC).
- Restrict allowed algorithms (e.g., only
RS256). - Implement proper token expiration.
What Undercode Say
APIs with weak JWT validation are prime targets for attackers. Always:
– Fuzz API endpoints with modified tokens.
– Monitor logs for unusual token usage.
– Use rate-limiting to prevent brute-force attacks.
Expected Output:
{
"error": "Invalid token",
"status": 401
}
Prediction:
As APIs grow, JWT misconfigurations will remain a leading cause of breaches. Developers must enforce strict token validation to prevent unauthorized access.
References:
Reported By: Abdelaziz Ahmed – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
