CVE-2026-9816

high

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

References

https://mattermost.com/security-updates

Details

Source: Mitre, NVD

Published: 2026-08-17

Updated: 2026-08-17

Risk Information

CVSS v2

Base Score: 8.7

Vector: CVSS2#AV:N/AC:L/Au:S/C:P/I:C/A:C

Severity: High

CVSS v3

Base Score: 8.3

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H