Issuer-Validation Bypass in joserfc Python Library
CVE-2026-75509

6.5MEDIUM

Key Information:

Vendor

Authlib

Status
Joserfc
Vendor
CVE Published:
24 August 2026

What is CVE-2026-75509?

The joserfc library, a Python implementation of JSON Object Signing and Encryption standards, is susceptible to an issuer-validation bypass. Versions prior to 1.7.3 of the library permit a list-valued 'iss' (issuer) claim that includes the expected issuer, thus allowing for improper membership matching. This defect could lead to an attacker exploiting the intended equality check for issuer validation, potentially enabling unauthorized access or manipulation of secured data. The issue has been resolved in version 1.7.3.

Affected Version(s)

joserfc < 1.7.3

References

https://github.com/authlib/joserfc/security/advisories/GH...
x_refsource_CONFIRM
https://github.com/authlib/joserfc/commit/76ee6a59bf5773c...
x_refsource_MISC

CVSS V3.1

Score:
6.5
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
High
Availability:
Low
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.