Kimai contains an authenticated improper authorization vulnerability in Team-related assignment APIs. A Teamlead who can edit their own team can use backend API endpoints to add users or activities that fall outside their intended visible or manageable scope, even when the frontend correctly hides those targets. This affects both team member assignment and team activity assignment. The issue is caused by treating "may edit this team" as equivalent to "may attach any referenced object to this team", without performing a second authorization check on the target user or activity.