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.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Pyjwt | Pyjwt_project | * | 1.5.0 (including) |
| Pyjwt | Ubuntu | devel | * |
| Pyjwt | Ubuntu | esm-infra/xenial | * |
| Pyjwt | Ubuntu | upstream | * |
| Pyjwt | Ubuntu | xenial | * |
| Pyjwt | Ubuntu | zesty | * |