CVE-2026-27656

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CVSS 3.1

6.1 medium

EPSS

<1%p8

Published

Mar 25, 2026 (Mar 25, 2026)

Modified

Jun 17, 2026

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

Vendors: mattermost
Products: mattermost server
Weakness: CWE-303
Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N

NVD CVE.org GitHub PoCs EPSS (0.2%)

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