JWT attacks
The payload is a claim list. The header is the attack. Verify what the server actually verifies: alg, kid, jku, and whether role or tenant claims are trusted unsigned.
Playbooks
- JWT Attacks - Forge or tamper JSON Web Tokens by abusing weak verification.
Gadgets
- JWT algorithm / key confusion - alg=none, RS-to-HS confusion, kid pointing at a file or a JWK URL you control, or a wildcard jku.
Payloads
- JWT Attacks - Probe weak verification. Confirm with jwt_tool. Try alg:none, RS256→HS256 key confusion, and kid path/SQL injection; crack HS256 secrets offline.
Bypasses
- JWT header / key tricks - The payload is a distraction. The header is the attack: alg, kid, jku, x5u, and whether the server fetches a key you control.
Checklists
- JWT / session tokens - The payload is a claim list. The header is the attack. Verify what the server actually verifies.
Tools
- jwt_tool - Swiss-army knife for JWTs: decode, tamper claims, and test the classic attacks - alg:none, key confusion (RS→HS), weak-secret cracking, and kid injection.
- hashcat - GPU hash cracker. JWT HS256, NTLM, phpass, and the rest. Identify the mode first (the hash-id util on this site helps), then crack offline hashes you are authorized to recover.
Questions
Is alg none still real?
On some libraries, yes. The server must accept the token, not just decode it. Prove a privileged claim change on an account you own.
Where do I look first?
alg, kid, jku/x5u, then email_verified / role / tenant_id. Refresh-token logout is a separate session bug.
This page is the public form of hunt_brief("jwt") on the MCP connector. Authorized testing only.