Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to properly validate user identity in the OpenID {{IsSameUser()}} comparison logic, which allows an attacker to take over arbitrary user accounts via an overly permissive substring matching flaw in the user discovery flow.. Mattermost Advisory ID: MMSA-2026-00590
CVSS Details
- CVSS 3.1 Base Score: 5.7
- CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N)
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