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CVE-2026-27656

MEDIUM CVSS: 5.7 Published: 2026-03-25 Modified: 2026-06-17

Description

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

Affected Platforms

Mattermost Mattermost Server

Weakness Type

CWE-303

References