Kimai before 2.63.0 contains a business logic / improper authorization vulnerability in the team update API endpoint (PATCH /api/teams/{id}), which removes all existing team members before validating the submitted replacement member list. An authenticated teamlead (or other user) with permission to edit a team can submit a malformed members payload; although Kimai returns a validation error, the existing membership rows have already been deleted. This bypasses the dedicated member-removal endpoint's protection against removing teamleaders and can leave a team with no members or teamleaders, disrupting team-based access control.