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CVE-2026-102266PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
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.
9.1 CRITICALEPSS 0.22%Not in KEVNVD: Analyzed
Overview
Severity
| Score | Severity | Version | Vector String |
|---|---|---|---|
| 9.1 | CRITICAL | 3.1NVD | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| 7.4 | HIGH | 3.1GitHub_M (CNA) | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
Details
- CVE ID
- CVE-2026-102266
- Status
- Analyzed
- Assigner (CNA)
- GitHub_M
- Published
- Sep 28, 2026
- Last modified
- 2026-10-07 20:55 UTC
- Weaknesses
- CWE-347 · Improper Verification of Cryptographic Signature
Affected Products
As published by the CNA in the CVE record.
jpadillapyjwt1 version range
- >= 2.13.0, < 2.14.0