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
INFO
Published Date :
2026-03-25T16:28:29.739Z
Last Modified :
2026-03-26T13:19:52.338Z
Source :
Mattermost
AFFECTED PRODUCTS
The following products are affected by CVE-2026-27656 vulnerability.
| Vendors | Products |
|---|---|
| Mattermost |
|
REFERENCES
Here, you will find a curated list of external links that provide in-depth information to CVE-2026-27656.
| URL | Resource |
|---|---|
| https://mattermost.com/security-updates |
|
CVSS Vulnerability Scoring System
Detailed values of each vector for above chart.
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact