CVE-2026-87998: Open WebUI: Non-admin users can delete admin-owned external knowledge connections via knowledge base deletion

External knowledge connections are created and owned by administrators, and are shared by every external knowledge base bound to them. Deleting an external knowledge base also removed that connection from the instance configuration, with no check on the caller’s role and no check for other knowledge bases still using it. Any authenticated user holding a write grant on a single external knowledge base could therefore wipe a shared connection that other knowledge bases depend on, and the dedicated administrator route for deleting a connection explicitly refuses that same operation while the connection is still in use.