Comment by smw
23 days ago
You literally can't access the internal devices with the NAT implementation on most consumer level router/access points except for packets addressed to the port mapped to an already open connection originating from the inside. This is almost guaranteed to be a random high port. There's no way to access any other port on an internal ip address.
That's equivalent to default-deny.
I think either you're just trying to "well-actually" us or you're confused.
I think understand what GP is saying; if you manage to get a packet to the internet port of the NAT router with a destination IP of e.g. 192.168.0.123, and the NAT router is running a generic IPv4 routing stack, it will dutifully route it to the internal network.
This can be done by compromising another host on the same link. It can also be done if anything on the same link (including the router itself) is running an improperly configured tunneling setup that lets the attacker send e.g. an IP-in-IP packet that gets unwrapped. The NAT has made it much harder to get a packet establishing an inbound connection to the router, but doesn't actually prevent the establishment of a connection should such a packet get there.
Compare to a default-deny firewall with public addresses on the LAN. Any inbound connections will be dropped, by definition; the lack of NAT makes it trivial to get a packet to the firewall itself, but once it's there, it won't get through.
I'm not. You literally can do this, provided there's no firewall. All you need to do is send the router a packet that's already addressed to a LAN machine, and in it goes. "NAT won't translate the packet" doesn't matter if the address is already set to an IP from the LAN.
Most consumer-level routers do have a firewall to prevent it from happening, and if they don't then people describe that router as being "grossly misconfigured" or as having a security vulnerability and similar things, so in practice it'll be blocked. But that's my point: they need the firewall to do the job precisely because NAT doesn't do it.