What is CVE-2026-14259?

CVE-2026-14259 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 4.3/10. Published 2026-09-14.

How severe is CVE-2026-14259?

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

Auth bypass in Mattermost

CVE-2026-14259

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to enforce board creation permissions when importing archive files which allows an authenticated non-guest team member to create Open or Private boards despite administrator restrictions via importing a crafted .boardarchive file. Mattermost Advisory ID: MMSA-2026-00712

Vulnerability class: Broken Access Control

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

Weakness classification (CWE)

CWE-862 — Missing Authorization

References

responsibledisclosure@mattermost.com (vendor-advisory)

Frequently asked questions

What is CVE-2026-14259?: CVE-2026-14259 is a medium-severity vulnerability in Mattermost, classified under Missing Authorization. CVSS score: 4.3/10. Published 2026-09-14.
How severe is CVE-2026-14259?: Medium severity. CVSS v3 base score is 4.3 out of 10.