CVE-2026-0999: Mattermost Server

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

Mattermost versions 11.1.x <= 11.1.2, 10.11.x <= 10.11.9, 11.2.x <= 11.2.1 fail to properly validate login method restrictions which allows an authenticated user to bypass SSO-only login requirements via userID-based authentication. Mattermost Advisory ID: MMSA-2025-00548

Affected products

• Mattermost Mattermost Server: from 10.11.0, before 10.11.10 (fixed in 10.11.10); from 11.1.0, before 11.1.3 (fixed in 11.1.3); from 11.2.0, before 11.2.2 (fixed in 11.2.2)

Published 2026-02-16. Last modified 2026-06-17.