Comment by lamontcg
1 month ago
Yeah, I think it is a bit more subtle of an issue than this flamewar always descends into.
There's people upthread arguing that every cellphone in the country is on IPv6 and nobody worries about it, but I'm certain there are thousands of people getting paid salaries to worry about that for you.
Meanwhile, the problem is about the level of trust in the consumer grade router sitting on my desk over there. With IPv4 NAT it is more likely that the router will break in such a way that I won't be able to access the internet. Having NAT break in such a way that it accidentally port forwards all incoming connection attempts to my laptop sitting behind it is not a likely bug or failure mode. If it does happen, it would likely only happen to a single machine sitting behind it.
OTOH, if my laptop and every other machine on my local subnet has a public IPv6 address on it, then I'm trusting that consumer grade router to never break in such a way that the firewall default allows all for some reason--opening up every single machine on my local subnet and every single listening port. A default deny flipping to a default allow is absolutely the kind of security bug that really happens and would keep me awake at night. And even if I don't go messing around with it and screw it up myself, there's always the possibility that a software bug in a firmware upgrade causes the problem.
I'd like to know what the solution to this is, other than blind trust in the router/firewall manufacturer or setting up your own external monitoring (and testing that monitoring periodically).
Instead of just screaming about how "NAT ISN'T SECURITY" over and over, I'd like someone to just explain how to mitigate the security concerns of firewall rulesets--when so very many of us have seen firewall rulesets be misconfigured by "professionals" at our $DAYJOBs. Just telling me that every IPv6 router should have default deny rules and nobody would be that incompetent to sell a router that wouldn't be that insecure doesn't give me warm fuzzies.
I don't necessarily trust NAT more, but a random port forward rule for all ports appearing against a given target host behind it is going to be a much more unusual kind of bug than just having a default firewall rule flipped to allow.
You could set up a monitoring solution that alerts you if one of your devices is suddenly reachable from the internet via IPv6. It will probably never fire an alert but in your case might help you sleep better. IPv6 privacy extensions could help you too.
In practice I don't think it's really an issue. The IPv6 firewall will probably not break in a way that makes your device reachable from the internet. Even if it would, someone would have to know the IPv6 address of the device they want to target - which means that you have to connect to a system that they have control of first, otherwise it's unlikely they'll ever get it. Lastly, you'd have to run some kind of software on that device that has a vulnerability which can be exploited via network. Combine all that and it gets so unlikely that you'll get hacked this way that it's not worth worrying about.