What is CVE-2026-15754?

CVE-2026-15754 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.2/10. Published 2026-08-17.

How severe is CVE-2026-15754?

Medium severity. CVSS v3 base score is 4.2 out of 10.

Auth bypass in Mattermost

CVE-2026-15754

Mattermost versions 11.7.x <= 11.7.6, 11.8.x <= 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC (attribute-based access control) policy assignments from channels outside their team via the policy unassign API after a channel has been moved to another team.. Mattermost Advisory ID: MMSA-2026-00718

Vulnerability class: Broken Access Control

CVSS v3 metric

CVSS v3 base score 4.2 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:H/A:N.

Affected products

Mattermost — versions 11.7.0, 11.8.0, 11.9.0

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory)

Frequently asked questions

What is CVE-2026-15754?: CVE-2026-15754 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.2/10. Published 2026-08-17.
How severe is CVE-2026-15754?: Medium severity. CVSS v3 base score is 4.2 out of 10.