CVE-2026-27656

MediumCVSS 6.1/10Last 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

Metrics

CVSS 3.1 6.1/10CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N

Weakness enumeration

CWE-303

Affected software

No affected versions have been published.

Timeline

Published: Mar 25, 2026
Last modified: Jun 17, 2026
NVD status: Analyzed

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