Vulnerability details
CVE-2026-120459
mpdavis python-jose
python-jose through 3.5.0 Authentication Bypass via Empty HMAC Key
CVSS 4.0
9.1Critical
Official description
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.
CVSS scores
| Score | Version | Source | Vector |
|---|---|---|---|
| 9.1Critical | 4.0 | CVEProject cvelistV5 (CNA) (VulnCheck) | 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 |
| 7.4High | 3.1 | CVEProject cvelistV5 (CNA) (VulnCheck) | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
Affected products
| Vendor | Product | Versions | Source |
|---|---|---|---|
| mpdavis | python-jose | v ≤ 3.5.0 | CVEProject cvelistV5 (CNA) |
References and advisories
4- https://github.com/mpdavis/python-jose/issues/398 issue-tracking
- https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/native.py technical-description
- https://github.com/mpdavis/python-jose/blob/3.5.0/jose/backends/cryptography_backend.py technical-description
- https://www.vulncheck.com/advisories/python-jose-through-3.5.0-authentication-bypass-via-empty-hmac-key third-party-advisory
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Details
- Published
- 2026-11-02
- Last updated
- 2026-11-09
- State
- Published
- Assigner (CNA)
- VulnCheck
- Kolun priority
- 18 · Low
Exploit prediction (EPSS)
0.25%
Probability of exploitation in 30 days
16.5%
Percentile (among all CVEs)
SSVC assessment (CISA)
- Automatable
- No
- Exploitation
- None
- Technical impact
- Total
Weaknesses (CWE)
- CWE-347Improper Verification of Cryptographic Signature