HIGH 8.3 NVD

CVE-2026-9816

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

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

References

https://mattermost.com/security-updates

Published: 2026-08-17 · Source: NVD · Feed updated: 2026-08-18

This high severity vulnerability with a CVSS score of 8.3 was published on 2026-08-17 via NVD.

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