Vulnerability in Mpdavis Python-Jose
CVE-2026-120459
python-jose through 3.5.0 contains an authentication bypass vulnerability that allows unauthenticated attackers to forge JWTs because HMACKey and CryptographyHMACKey accept zero-length HMAC secrets. When an application's HS256/HS384/HS512 verification key resolves to empty, such as an oct JWK with empty k, attackers can forge tokens with arbitrary claims that jwt.decode accepts.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/mpdavis/python-jose/issues/398 (issue-tracking)
- github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.py (technical-description)
- github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.py (technical-description)
- www.vulncheck.com/advisories/python-jose-through-3.5.0-authentication-bypass-vi… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-120459?
- CVE-2026-120459 is a high-severity vulnerability in Mpdavis Python-Jose, classified under Improper Verification of Cryptographic Signature. CVSS score: 7.4/10. Published 2026-11-02.
- How severe is CVE-2026-120459?
- High severity. CVSS v3 base score is 7.4 out of 10.