CVE-2026-10527 Boards plugin retains Board Admin rights for users demoted to System Guest

Mattermost versions 11.7.x = 11.7.6, 10.11.x = 10.11.21, 11.8.x = 11.8.3 fails to reconcile SchemeAdmin flags with a user's current role which allows a user demoted to System Guest to retain Board Admin privileges and perform admin-only operations via the Boards REST API or UI.. Mattermost Adviso...