Auth bypass in Mattermost
CVE-2026-91181
Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 Fail to sanitize Team objects returned by the data retention teams endpoint which allows an authenticated user holding only the read-only Data Retention Policy permission to obtain a private team's secret invite_id and email, and use it to join the team without authorization, via GET /api/v4/data_retention/policies/{policy_id}/teams.. Mattermost Advisory ID: MMSA-2026-00702
Vulnerability class: Broken Access Control
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:N.
Affected products
Weakness classification (CWE)
References
- responsibledisclosure@mattermost.com (vendor-advisory)
Frequently asked questions
- What is CVE-2026-91181?
- CVE-2026-91181 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 6.5/10. Published 2026-09-14.
- How severe is CVE-2026-91181?
- Medium severity. CVSS v3 base score is 6.5 out of 10.