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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-102266
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-28 21:17:14 UTC
Updated2026-09-28 21:17:14 UTC
DescriptionPyJWT 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.

Risk And Classification

Primary CVSS: v3.1 7.4 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Problem Types: CWE-347 | CWE-347 CWE-347: Improper Verification of Cryptographic Signature

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Jpadilla Pyjwt affected >= 2.13.0, < 2.14.0 Not specified

References

ReferenceSourceLinkTags
github.com/jpadilla/pyjwt/releases/tag/2.14.0 [email protected] github.com
github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r [email protected] github.com
github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c [email protected] github.com
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