CVE-2026-15754 Missing per-channel team-scope check in ABAC access control policy unassign allows cross-team policy removal

Mattermost versions 11.7.x = 11.7.6, 11.8.x = 11.8.3 The access control policy unassign endpoint fails to re-validate that each target channel still belongs to the requesting admin's team, which allows an authenticated team administrator to remove ABAC attribute-based access control policy...