JWT Security Review

Review JWT-based authentication end to end.

Review Areas

Algorithm Handling

• Pin the expected algorithm server-side; reject alg: none outright
• RS256→HS256 confusion: if the server verifies HMAC using the public key as the secret, an attacker can forge tokens. Confirm verification uses the correct key type per algorithm
• Watch for jku/x5u header injection where the server fetches keys from an attacker-controllable URL
• kid injection: path traversal or SQL/Command injection in key lookup

Key and Secret Strength

• HS256 secrets: ≥32 bytes of entropy, not from wordlists (jwt-tools crack mode)
• Keys rotated; old keys revoked rather than just unused