CVE-2026-0999 Authentication bypass via userID login when email and username login are disabled

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...

Authentication Bypass

Mattermost is vulnerable to Authentication Bypass. The vulnerability is due to improper enforcement of multi-factor authentication MFA due to a flaw that allows authenticated attackers to bypass MFA protections via API requests to plugin-specific routes...