Incorrect Implementation of Authentication Algorithm

Overview github.com/mattermost/mattermost/server/channels/app is a private-cloud Slack alternative Affected versions of this package are vulnerable to Incorrect Implementation of Authentication Algorithm via the userID authentication. An attacker can gain unauthorized access by leveraging...

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...

CVE-2026-0999

Technical details beyond the summary are not provided in the supplied documents. Monitor for updates from Mattermost advisory MMSA-2025-00548.