CVE-2026-27659
Mattermost doesn't properly validate CSRF tokens
4.6
MEDIUM
CVSS 3.1
EPSS 0.03%
Description
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to properly validate CSRF tokens in the /api/v4/access_control_policies/{policy_id}/activate endpoint, which allows an attacker to trick an admin into changing access control policy active status via a crafted request. Mattermost Advisory ID: MMSA-2026-00578
How to fix CVE-2026-27659
To remediate CVE-2026-27659, upgrade the affected package to a fixed version below.
- —upgrade to 11.4.1 or later
Is CVE-2026-27659 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- >= 11.4.0-rc1, < 11.4.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM4.6 | CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N |