Comment by bandrami
17 days ago
If your public IP from your ISP is 12.13.14.15, and your internal block is 192.168.0.0/24, then your ISP can send a packet to 12.13.14.15 destined for 192.168.0.7, and without a firewall your router will happily forward it. An attacker who can convince intervening routers to send traffic destined for 192.168.0.7 to 12.13.14.15 (and these attacks do exist, particularly over UDP) can also do that.
You're using somewhat sloppy terminology that will confuse things. An IP packet can't be addressed both to 12.13.14.15 AND to 192.168.0.7.
The realistic attack here is that your ISP sends a packet with destination address 192.168.0.7 to the MAC of your router (the MAC that corresponds to 12.13.14.15). This is a realistic attack scenario if the device that your router connects directly to gets compromised (either by an attacker or by the ISP itself).
Getting a public route that would take packets destined for 192.168.0.7 to reach your router over the Internet is far more unlikely.
True, the frame is addressed to the router's hw interface but I'm talking to people who think NAT drops traffic so I figured keep it simple
But, yes, the ISP (or whoever has compromised/suborned/social engineered the ISP) is absolutely the main worry here and I don't understand how people are dismissing that so easily
> I don't understand how people are dismissing that so easily
Because that’s not where 99.9999% of attacks come from
Fire up a web server on a public ipv4 address and you’ll get hundreds of requests per day from bots probing endpoints for vulnerabilities. Same thing goes for weak passwords on an SSH endpoint.
Okay, so not only do you have to create a bogus packet, you have to convince every piece of equipment in between you and the end user to collude with it, in the hopes that the final router is so woefully misconfigured as to act upon it?
The ISP is the primary threat vector here (do you trust yours? Along with their contractors and anyone who might have compromised them?). But like I said route-poisoning attacks do exist.
yeah but the likelihood of this is incredibly remote. It would shock me if ISPs didn't have alarms going off if RFC1918 space was suddenly routable within their BGP table.
Not to mention the return packet would be NAT'd so the attacker would have to deal with that complication.
15 replies →
Yes, I trust everyone who works at it, mostly because I know where they live.
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No, the router will only forward it with specific implementations that don’t isolate routing tables between the external and internal. Or an easier approach is just a stateless ACL on the external interface. Neither are a stateful firewall.