python-jose through 3.5.0 improperly validates asymmetric keys during HMAC init, accepting DER-encoded public keys without PEM armor/SSH prefixes. An attacker who has the service public key can forge HS256 JWTs that verify if allowed algorithms are not explicitly restricted, enabling auth bypass/account takeover. Mitigate by pinning allowed algs (avoid HS*) and upgrading when a fix is available.