CVE-2026-27656
MEDIUM
NVD
CVSS Score
5.7
Severity
MEDIUM
Published
Mar 25, 2026
Vendor
unknown
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