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

CVSS v3 5.7 MEDIUM

5.7^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 0.5 / Impact : 5.2

Attack Vector NETWORK

Attack Complexity HIGH

Privileges Required HIGH

User Interaction REQUIRED

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://mattermost.com/security-updates	Vendor Advisory

Configurations

Configuration 1 (hide)

OR	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::
	cpe:2.3:a:mattermost:mattermost_server::::::::

History

No history.

Information

Published : 2026-03-25 17:16

Updated : 2026-03-26 18:51

NVD link : CVE-2026-27656

Mitre link : CVE-2026-27656

CVE.ORG link : CVE-2026-27656

JSON object : View

Products Affected

mattermost

mattermost_server

CWE

CWE-303

Incorrect Implementation of Authentication Algorithm

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