A user plane network entity of a 5G core network performs: obtaining GPRS Tunneling Protocol User Plane (GTP-U) tunneling information of a new or updated protocol data unit (PDU) session from a control plane network entity of the 5G core network; and adjusting according to the obtained GTP-U tunneling information a GTP-U firewall for selectively allowing to pass through only GTP-U traffic concerning GTP-U tunnels defined by the GTP-U tunneling information. The control plane network entity performs: obtaining from control plane signaling the GTP-U tunneling information and communicating same to the GTP-U firewall. A system containing the user plane network entity and the control plane network entity is also disclosed.