CVE-2026-14259: Mattermost Server

Medium severity, CVSS 4.3. EPSS: 0.2% chance of exploitation in the next 30 days.

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

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.23 (fixed in 10.11.23); from 11.7.0, before 11.7.8 (fixed in 11.7.8); from 11.8.0, before 11.8.5 (fixed in 11.8.5); from 11.9.0, before 11.9.1 (fixed in 11.9.1)

Published 2026-09-14. Last modified 2026-10-07.