by Kastro
Paper/Archive/CVE-2026-102266

CVE-2026-102266

jpadilla pyjwt — PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation

EPSS 0.2%public exploitCVSS 9.1
critical.is priorityof 100
40
CVSS 9.1 (NVD)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 13.2.132 × 202.6Exploit: SSVC poc+1010.0SSVC exploitation: poc+100.0
Description · from the CVE record

PyJWT is a Python implementation of JSON Web Token standards. From 2.13.0 until 2.14.0, HMACAlgorithm.from_jwk is affected because PyJWK verification path used the decoded key without applying prepare_key validation. This occurs when a trusted JWK Set contains an oct entry with an empty k value. As a result, an attacker signs an HMAC token with the same zero-length key accepted by PyJWT. Consequently, forged token can carry arbitrary authenticated claims. This issue is fixed in version 2.14.0.

Affected

ProductAffectedFixed inSource
pyjwt>= 2.13.0, < 2.14.0–CNA

Scores by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
GitHub_M (CNA)7.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: poc · Automatable: no · Technical impact: total

References

exploitgithub.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3rrefgithub.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934crefgithub.com/jpadilla/pyjwt/releases/tag/2.14.0