CVE-2026-102271 PyJWT: Public keys in DER form are accepted as HMAC secrets, bypassing the CVE-2022-29217 guard
Attackers can forge HMAC tokens by supplying DER public keys as secrets, bypassing algorithm guards in PyJWT applications mixing HMAC and asymmetric algorithms.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-102271?
CVE-2026-102271 is a high-severity vulnerability in jpadilla pyjwt, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-347
Which versions are affected by CVE-2026-102271?
3 open source packages ship an affected version, including pyjwt. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pyjwt PyPI | From 2.4.0 | 2.14.0 |
pyjwt PyPI | From 2.4.0 | 2.14.0 |
pyjwt PyPI | From 2.4.0 | 2.14.0 |
Products include Pyjwt Project Pyjwt.
How do I fix CVE-2026-102271?
Upgrade pyjwt to 2.14.0 or later.
Is CVE-2026-102271 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-102271 exists.
Other vulnerabilities in jpadilla pyjwt
- CVE-2026-102268 PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard
- CVE-2026-32597 PyJWT accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
- CVE-2026-102266 PyJWK accepts empty HMAC keys, bypassing PyJWT's empty-key validation
- CVE-2026-102267 PyJWT: PyJWKClient follows redirects when fetching JWKS
- CVE-2026-102272 PyJWT BOM Bypass
Sources
Also known as AZL-105221, CLEANSTART-2026-PD49878, CLEANSTART-2026-XO84437, DEBIAN-CVE-2026-102271, ECHO-1994-4c86-f69b, GHSA-p4g4-x82p-q773 and 28 more.