UPNP and a dozen other NAT defeating tactics exist and have since the early 2000s. NAT translates addresses. Thinking a non-routable range is safe because it's behind NAT is at this point grossly ignorant of how modern network equipment works. It's kind of like port-knocking; yes it makes the attack slightly harder, but doesn't prevent it.

e.g. symmetric NAT exists and often doesn't come with a stateful firewall. Just because the linux box with iptables is protecting your network uses NAT doesn't mean NAT is doing the heavy lifting here. I can see the OMG MY PRIVACY crew is out in force here apparently misunderstanding that NAT does not do that either. I mean, we can explain things to you, but we can't understand it for you.

It doesn't confer much since it COULD be only NAT and no firewall.

It's INCREDIBLY unlikely to find a case of that in the wild, but possible.

A common example of a host that might have such an address but lacks that sort of security is anything as the default route for inbound packets, E.G. like you'd want your _own_ router / firewall rather than the ISP's modem.

rightly