VULNERABILITY INTELLIGENCE

CVE-2026-9816

CVSS score8.3 HIGH
EPSS probability0.35%
CISA KEVNot currently listed
Published2026-08-17
Last modified2026-08-19
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H

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

Weakness classification

  • responsibledisclosure@mattermost.com: CWE-863

Primary references