CVE-2026-9816
Insufficient server-side validation of board member role fields permits privilege escalation
CVSS Score
8.3
EPSS Score
0.0%
EPSS Percentile
0th
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
| CWE | CWE-863 |
| Vendor | mattermost |
| Product | mattermost |
| Published | Aug 17, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
High
Affected Versions
Mattermost / Mattermost
11.7.0 ≤ 11.7.6 10.11.0 ≤ 10.11.21 11.8.0 ≤ 11.8.3
Credits
kamil-sawicki