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Vulnerability record · CVE-2026-102266 · published 28 September 2026

CVE-2026-102266: Pyjwt project pyjwt improper verification of cryptographic signature vulnerability

Pyjwt Project · Pyjwt

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 CVSS 3.1 Critical EPSS 0.18% · top 92.9% CWE-347 · Improper verification of cryptographic signature
9.1CVSS 3.1 base score
0.18%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References, 2 tagged exploit
7 Oct 2026Last modified by NVD

Description

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/jpadilla/pyjwt/commit/f91ed44dd65baaf457f4b3353ed35e98a753934c Patch
https://github.com/jpadilla/pyjwt/releases/tag/2.14.0 ProductRelease Notes
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r ExploitVendor Advisory
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-9j54-fg26-wv3r ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-102266), CISA KEV, FIRST EPSS (scores of 2026-10-08). This page is refreshed as NVD updates the record.