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Vulnerability record · CVE-2026-102271 · published 28 September 2026

CVE-2026-102271: Pyjwt project pyjwt improper verification of cryptographic signature vulnerability

Pyjwt Project · Pyjwt

PyJWT is a Python implementation of JSON Web Token standards. From 2.4.0 until 2.14.0, PyJWT HMACAlgorithm.prepare_key is affected because asymmetric-key guard relies on textual markers that are absent from DER encoding. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a DER public key as the shared verification key. As a result, PyJWT uses public DER bytes as an HMAC secret. Consequently, an attacker who knows the public key can forge authenticated HMAC tokens. This issue is fixed in version 2.14.0.

7.4 CVSS 3.1 High EPSS 0.18% · top 93.0% CWE-347 · Improper verification of cryptographic signature
7.4CVSS 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
6 Oct 2026Last modified by NVD

Description

PyJWT is a Python implementation of JSON Web Token standards. From 2.4.0 until 2.14.0, PyJWT HMACAlgorithm.prepare_key is affected because asymmetric-key guard relies on textual markers that are absent from DER encoding. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a DER public key as the shared verification key. As a result, PyJWT uses public DER bytes as an HMAC secret. Consequently, an attacker who knows the public key can forge authenticated HMAC tokens. This issue is fixed in version 2.14.0.

CVSS:3.1/AV:N/AC:H/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/2798504fa2663364573cf2d1043d8d7fef389499 Patch
https://github.com/jpadilla/pyjwt/releases/tag/2.14.0 ProductRelease Notes
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-p4g4-x82p-q773 ExploitPatchVendor Advisory
https://github.com/jpadilla/pyjwt/security/advisories/GHSA-p4g4-x82p-q773 ExploitPatchVendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2026-102271), CISA KEV, FIRST EPSS (scores of 2026-10-11). This page is refreshed as NVD updates the record.