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CVE-2026-120459python-jose through 3.5.0 Authentication Bypass via Empty HMAC Key
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.
9.1 CRITICALEPSS 0.25%Not in KEVNVD: Awaiting Analysis
Overview
Severity
| Score | Severity | Version | Vector String |
|---|---|---|---|
| 9.1 | CRITICAL | 4.0VulnCheck (CNA) | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N |
| 7.4 | HIGH | 3.1VulnCheck (CNA) | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
Details
- CVE ID
- CVE-2026-120459
- Status
- Awaiting Analysis
- Assigner (CNA)
- VulnCheck
- Published
- Nov 2, 2026
- Last modified
- 2026-11-02 19:14 UTC
- Weaknesses
- CWE-347 · Improper Verification of Cryptographic Signature
Affected Products
As published by the CNA in the CVE record.
mpdavispython-jose1 version range
- through 3.5.0
References
- github.com https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.py
- github.com https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.py
- github.com https://github.com/mpdavis/python-jose/issues/398
- vulncheck.com https://www.vulncheck.com/advisories/python-jose-through-3.5.0-authentication-bypass-via-empty-hmac-key