CVE-2026-0999
MEDIUMCVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Lifecycle Timeline
3Description
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
Analysis
Mattermost Server versions 11.1.x through 11.1.2, 10.11.x through 10.11.9, and 11.2.x through 11.2.1 inadequately enforce login method restrictions, permitting authenticated users to circumvent SSO-only requirements by authenticating with a userID instead. This allows an attacker with valid credentials to gain unauthorized access to accounts restricted to single sign-on authentication. …
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Remediation
Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.
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External POC / Exploit Code
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