PyJWT Project PyJWT any version

In PyJWT 1.5.0 and below the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format would be allowed because it is prefaced with the string `-----BEGIN RSA PUBLIC KEY-----` which is not accounted for. This enables symmetric/asymmetric key confusion attacks against users using the PKCS1 PEM encoded public keys, which would allow an attacker to craft JWTs from scratch.

Key confusion through non-blocklisted public key formats in PyJWT

PyJWT accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)

PyJWT: Public-key JWK accepted as HMAC secret enables forged HS256 tokens when mixed families are allowed

PyJWT: Algorithm allow-list bypass when decoding with `PyJWK` / `PyJWKClient` keys

PyJWT: Unauthenticated DoS via unbounded Base64URL decoding of unused payload segment in b64=false detached JWS

PyJWKClient: missing scheme allowlist enables SSRF + token forgery via file://, ftp://, data: schemes

PyJWT: PyJWKClient unbounded JWKS endpoint requests via attacker-controlled kid values (DoS)