CVE-2026-102946: authlib joserfc Authentication Bypass by Spoofing

Vulnerability summary

CVE-2026-102946 is a critical (CVSS 9.1) Authentication Bypass by Spoofing vulnerability in authlib joserfc. EPSS estimates a 0.12% chance of exploitation in the next 30 days, higher than 1.5% of scored vulnerabilities.

Timeline

1. 15-10-2026
   PublishedVulnerability first disclosed.
2. 15-10-2026
   Last modifiedVulnerability information updated.

Description

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to 1.7.4, joserfc.jws.deserialize_json() accepts a JWS General JSON Serialization with an empty signatures array as authenticated. The verify_general_json() loop performs no iterations for the empty array and returns success because no signature check failed, allowing an attacker without a signing key to supply an arbitrary payload that relying applications may treat as authentic. The issue affects the General JSON Serialization path; compact JWS and JWT decoding, Flattened JSON serialization, and JWE JSON processing do not follow this vulnerable path. This issue is fixed in version 1.7.4.

• CWE-290Authentication Bypass by SpoofingThis attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
• CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
• CWE-347Improper Verification of Cryptographic SignatureThe product does not verify, or incorrectly verifies, the cryptographic signature for data.