CVE-2026-9816
Published:August 17, 2026
Updated:August 31, 2026
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate BoardMember.Scheme* fields server-side on insert and archive-import paths which allows a board editor or non-guest team member to grant board admin to arbitrary users via POST /api/v2/boards/{boardID}/members and POST /api/v2/teams/{teamID}/archive/import.. Mattermost Advisory ID: MMSA-2026-00685
Affected Packages
https://github.com/mattermost/mattermost-plugin-boards.git (GITHUB):
Affected version(s) >=v9.0.0 <v9.2.6Fix Suggestion:
Update to version v9.2.6github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.7.0 <v11.7.7Fix Suggestion:
Update to version v11.7.7github.com/mattermost/mattermost (GO):
Affected version(s) >=v10.11.0 <v10.11.22Fix Suggestion:
Update to version v10.11.22github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.8.0 <v11.8.4Fix Suggestion:
Update to version v11.8.4Related Resources (3)
Do you need more information?
Contact UsCVSS v4
Base Score:
7.2
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
LOW
User Interaction
NONE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
HIGH
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
8.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
LOW
Integrity
HIGH
Availability
HIGH
Weakness Type (CWE)
Incorrect Authorization
EPSS
Base Score:
0.26