What is CVE-2026-82920?

CVE-2026-82920 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.5/10. Published 2026-09-14.

How severe is CVE-2026-82920?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Auth bypass in Mattermost

CVE-2026-82920

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 fail to enforce authorization boundaries on the access control policy update endpoint which allows a channel or team administrator to detach a system-assigned ABAC parent policy via a crafted PUT /api/v4/access_control_policies request with an empty imports list.. Mattermost Advisory ID: MMSA-2026-00724

Vulnerability class: Broken Access Control

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N.

Affected products

Mattermost

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory)

Frequently asked questions

What is CVE-2026-82920?: CVE-2026-82920 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.5/10. Published 2026-09-14.
How severe is CVE-2026-82920?: Medium severity. CVSS v3 base score is 5.5 out of 10.