Moole Vulnerability Database

Find real vulnerabilities before they ship

Medium

CVE-2026-27656

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

VectorNETWORK

PublishedMar 25, 2026, 17:16

Published Byresponsibledisclosure@mattermost.com

Base Score

Score6.1

Affected Versions

Package (Ecosystem)IntroducedFixedLimit

github.com/mattermost/mattermost-server(Go)11.4.0-rc111.4.1N/A

github.com/mattermost/mattermost-server(Go)11.3.0-rc111.3.2N/A

github.com/mattermost/mattermost-server(Go)11.2.0-rc111.2.4N/A

github.com/mattermost/mattermost-server(Go)10.11.0-rc110.11.12N/A

github.com/mattermost/mattermost/server/v8(Go)8.0.0-20260105080200-d27a2195068d8.0.0-20260217110922-b7d4a1f1f59bN/A

References

https://mattermost.com/security-updates

Weakness Type

CWE-303

CVSS Metrics

Base Score

6.1

Vector String

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

Base SeverityMedium

Version

3.1

Attack Vector (AV)

NETWORK