Kanboard through 1.2.52, fixed in commit 564cc30, BoardAjaxController save() method (used by the kanban board drag-and-drop endpoint) validates the caller's role on the attacker-supplied project_id but never verifies that the supplied task_id actually belongs to that project. Because task identifiers are sequential integers shared across the entire instance, any authenticated user who is a member of at least one project can enumerate and move (corrupt/hide) tasks belonging to any other project on the same instance, including private projects they have no membership or role on.