VULNERABILITY INTELLIGENCE

CVE-2026-27656

CVSS score5.7 MEDIUM
EPSS probability0.18%
CISA KEVNot currently listed
Published2026-03-25
Last modified2026-06-17
CVSS vectorCVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:H/I:H/A:N

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

Weakness classification

  • responsibledisclosure@mattermost.com: CWE-303

Primary references