Assuming the router is somehow allowing NAT punctures or port forwarding, or if there is no router, then any easily compromised device will be compromised withi

Assuming the router is somehow allowing NAT punctures or port forwarding, or if there is no router, then any easily compromised device will be compromised within 5 minutes of connecting it to the Internet. Usually much less than 5 minutes. There's just that much Internet scanning. If NAT is configured properly, then there is no risk.