Description
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 products
mattermost: mattermost server
References1
- mattermost.com/security-updates Vendor Advisory
Metrics
- CVSS 3.1
-
8.3
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H - EPSS — exploit probability
- 0% percentile: 29 · as of 11 November 2026
- CWE
- CWE-863
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