What is CVE-2026-27659?

CVE-2026-27659 is a medium-severity vulnerability in Mattermost, classified under Cross-Site Request Forgery (CSRF). CVSS score: 4.6/10. Published 2026-03-25.

How severe is CVE-2026-27659?

Medium severity. CVSS v3 base score is 4.6 out of 10.

CSRF in Mattermost

CVE-2026-27659

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…

Vulnerability class: CSRF (Cross-Site Request Forgery)

EPSS: 0.000 (9.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 4.6 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N.

Affected products

Mattermost — versions 11.2.0, 10.11.0, 11.4.0

Weakness classification (CWE)

CWE-352 — Cross-Site Request Forgery (CSRF)

References

MMSA-2026-00578 (vendor-advisory)

Frequently asked questions

What is CVE-2026-27659?: CVE-2026-27659 is a medium-severity vulnerability in Mattermost, classified under Cross-Site Request Forgery (CSRF). CVSS score: 4.6/10. Published 2026-03-25.
How severe is CVE-2026-27659?: Medium severity. CVSS v3 base score is 4.6 out of 10.