JWT algorithm / key confusion
The token is a gadget until you can mint one the server accepts. Decode first, then test the header fields, not the payload.
Tags: jwt, ato, ssrf
Typical severity: P1-P3
What it becomes
alg=none, RS-to-HS confusion, kid pointing at a file or a JWK URL you control, or a wildcard jku.
Where to look
Authorization: Bearersession cookieaccess_token queryWebSocket first message
Chains
- Priv-esc / ATO — Forge sub / role / tenant and replay.
- SSRF — jku / x5u URL is fetched server-side.
Notes
- Use the JWT tamper box on /utils/ and jwt_tool on the host. Do not brute-force HS secrets against production without the program allowing it.