CVE-2026-9816

Mattermost 11.7.x (≤11.7.6), 10.11.x (≤10.11.21), and 11.8.x (≤11.8.3) lack server-side validation of BoardMember.Scheme* fields on insert and archive-import paths, allowing board editors or non-guest team members to grant Board Admin to arbitrary users via POST /api/v2/boards/{boardID}/members a...