CVE-2017-11424: PyJWT vulnerable to key confusion attacks

May 13, 2022 (updated October 15, 2024)

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.

References

github.com/advisories/GHSA-r9jw-mwhq-wp62
github.com/jpadilla/pyjwt
github.com/jpadilla/pyjwt/pull/277
github.com/pypa/advisory-database/tree/main/vulns/pyjwt/PYSEC-2017-24.yaml
nvd.nist.gov/vuln/detail/CVE-2017-11424

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