What is CVE-2026-75509?

CVE-2026-75509 is a medium-severity vulnerability in Authlib Joserfc, classified under Authentication Bypass by Spoofing. CVSS score: 6.5/10. Published 2026-08-24.

How severe is CVE-2026-75509?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Authlib Joserfc

CVE-2026-75509

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.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N.

Affected products

Authlib Joserfc — versions < 1.7.3

Weakness classification (CWE)

References

security-advisories@github.com (x_refsource_MISC)
security-advisories@github.com (x_refsource_CONFIRM)

Frequently asked questions

What is CVE-2026-75509?: CVE-2026-75509 is a medium-severity vulnerability in Authlib Joserfc, classified under Authentication Bypass by Spoofing. CVSS score: 6.5/10. Published 2026-08-24.
How severe is CVE-2026-75509?: Medium severity. CVSS v3 base score is 6.5 out of 10.