jwt-attack-methodology

JWT authentication security testing is performed by decoding tokens and executing targeted attacks like none-alg bypass, weak-key brute force, claims tampering, RS256→HS256 algorithm confusion, and jku/x5u header injections.

RS256 to HS256 algorithm confusion is an attack vector where a token using asymmetric RS256 is altered to symmetric HS256, allowing the attacker to sign new tokens using the server's public key as the HMAC secret.

To brute force a weak JWT secret, you decode the token and use utilities like hashcat, john, c-jwt-cracker, or jwt_tool to perform dictionary attacks against the HMAC signature to recover the signing key.

Yes, you can perform kid injection attacks on JWT headers by manipulating the key ID parameter to exploit SQL injection, path traversal, or command injection vulnerabilities within the token validation logic.

Executing a JWT attack methodology requires a JWT toolkit like PyJWT for decoding and signing tokens, alongside brute-force utilities such as hashcat, john, jwt_tool, and flask-unsign for cracking secrets.

You should check for jku or x5u header injection when a JWT header contains URL references for public keys or certificates, allowing you to replace these URLs to point to an attacker-controlled server hosting a malicious key.