What’s Vulnerable › Vulnerabilities

CVE-2026-102268: PyJWT: Asymmetric-PEM detection bypass: whitespace/line-ending-mutated public keys skip the HS/asymmetric confusion guard

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-09-28 · updated 2026-10-07
• Weakness: CWE-347

Description

PyJWT is a Python implementation of JSON Web Token standards. Prior to 2.14.0, is_pem_format in jwt/utils.py is affected because is_pem_format does not recognize every PEM representation accepted by the cryptography loader. This occurs when an application mixes HMAC and asymmetric algorithms and supplies a mutated public-key PEM as raw key bytes. As a result, HMACAlgorithm.prepare_key treats the unrecognized asymmetric public key 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 products

• jpadilla pyjwt: before 2.14.0 — fixed in 2.14.0

How to fix

Upgrade to a fixed version: jpadilla pyjwt 2.14.0. Check the vendor advisory for mitigations.

References

• https://github.com/jpadilla/pyjwt/commit/8b4e233a22206b34ec1186e912e75c0b2396ac07
• https://github.com/jpadilla/pyjwt/releases/tag/2.14.0
• https://github.com/jpadilla/pyjwt/security/advisories/GHSA-ffc3-869f-jxw9
• https://github.com/jpadilla/pyjwt/security/advisories/GHSA-ffc3-869f-jxw9

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