CVE-2026-75509

joserfc claim-validation bypass via array-typed single-string claims (iss/sub/jti)

State: Published
Severity: 6.5 Medium
Published: Aug 24, 2026
Updated: Aug 25, 2026
Reserved: Aug 17, 2026

Description

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass an intended equality check and enabling issuer-validation bypass. This issue is fixed in version 1.7.3.

Scores

CVSS	Score	Vector	Source
3.1	6.5 Medium	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N	GitHub_M

Weaknesses

CWE-290 Authentication Bypass by Spoofing
CWE-345 Insufficient Verification of Data Authenticity

Affected Products

Product	Versions
joserfcauthlib	< 1.7.3Affected

References

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