CVE-2026-102271

PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard

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.

Affected

jpadilla · pyjwt

CVSS v3.1 GITHUB

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

EPSS

0.18% chance of exploitation in the next 30 days, 7th percentile

Published

2026-09-28

Updated

2026-10-01

Proof-of-concept exploits (1)

• advisories/GHSA-p4g4-x82p-q773

Security advisories

• jpadilla/pyjwt/security/advisories/GHSA-p4g4-x82p-q773
• jpadilla/pyjwt/commit/2798504fa2663364573cf2d1043d8d7fef389499

References

• CVE Record
• NVD entry