What is CVE-2026-4274?

CVE-2026-4274 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.4/10. Published 2026-03-26.

How severe is CVE-2026-4274?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Auth bypass in Mattermost

CVE-2026-4274

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 restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user…

Vulnerability class: Broken Access Control

EPSS: 0.000 (12.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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-863 — Incorrect Authorization

References

MMSA-2026-00574 (vendor-advisory)

Frequently asked questions

What is CVE-2026-4274?: CVE-2026-4274 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 5.4/10. Published 2026-03-26.
How severe is CVE-2026-4274?: Medium severity. CVSS v3 base score is 5.4 out of 10.