---
id: CVE-2026-75509
title: >-
  joserfc is a Python library that provides an implementation of several JSON
  Object Signing and Encryption (JOSE) standards
summary: >-
  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…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N'
cwe:
  - CWE-290
  - CWE-345
published: '2026-08-24'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T21:06:39.057'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-75509'
references:
  - url: >-
      https://github.com/authlib/joserfc/commit/76ee6a59bf5773c0af00b99076c5e199031f97f1
    label: security-advisories@github.com
  - url: 'https://github.com/authlib/joserfc/security/advisories/GHSA-r74j-q665-7rpj'
    label: security-advisories@github.com
  - url: 'https://github.com/authlib/joserfc/security/advisories/GHSA-r74j-q665-7rpj'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
epss: 0.00124
epssPercentile: 0.01826
ingestedAt: '2026-09-09T21:22:45.549Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.