Kimai is a web-based multi-user time-tracking application. Prior to version 2.51.0, "GET /api/invoices/{id}" only checks the role-based view_invoice permission but does not verify the requesting user has access to the invoice's customer. Any user with ROLE_TEAMLEAD (which grants view_invoice) can read all invoices in the system, including those belonging to customers assigned to other teams. This issue has been patched in version 2.51.0.