What is CVE-2026-4055?

CVE-2026-4055 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.3/10. Published 2026-05-21.

How severe is CVE-2026-4055?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Auth bypass in Mattermost

CVE-2026-4055

Mattermost versions 11.5.x <= 11.5.1 fail to validate team-level run_create permission against the target team when creating a playbook run which allows an authenticated team member to create runs in teams where they lack permission via sp…

Vulnerability class: Broken Access Control

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

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N.

Affected products

Mattermost — versions 11.5.0, 11.6.0, 11.5.2
Mattermost Mattermost_server

Weakness classification (CWE)

CWE-863 — Incorrect Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-4055?: CVE-2026-4055 is a medium-severity vulnerability in Mattermost, classified under Incorrect Authorization. CVSS score: 4.3/10. Published 2026-05-21.
How severe is CVE-2026-4055?: Medium severity. CVSS v3 base score is 4.3 out of 10.