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
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Privileges Required
High
Admin privileges needed
User Interaction
Required
User action required
Impact Assessment
Confidentiality
High
Complete data leak
Integrity
High
Complete data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
Vulnerable Products 4
| Configuration | From (including) | Up to (excluding) |
|---|---|---|
|
Mattermost Mattermost_Server
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
|
10.11.0
|
10.11.12
|
|
Mattermost Mattermost_Server
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
|
11.2.0
|
11.2.4
|
|
Mattermost Mattermost_Server
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
|
11.3.0
|
11.3.2
|
|
Mattermost Mattermost_Server
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*
|
11.4.0
|
11.4.1
|