CVE-2026-27656

MEDIUM

5.7

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

CVE Details

CVSS v3.1 Score5.7

SeverityMEDIUM

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

Attack VectorNETWORK

ComplexityHIGH

Privileges RequiredHIGH

User InteractionREQUIRED

Published3/25/2026

Last Modified3/26/2026

Sourcenvd

Honeypot Sightings0

Affected Products

mattermost:mattermost_server

Weaknesses (CWE)

CWE-303

References

https://mattermost.com/security-updates(responsibledisclosure@mattermost.com)

IOC Correlations

No correlations recorded

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