Comment by muvlon
19 days ago
It's sad how much of this thread of supposed hackers comes from people who are simply parroting this dogma because it has been drilled into them. People were even preaching this before IPv6 privacy extensions came into use, either downplaying the privacy issues or outright telling people they were bad for wanting privacy because IPv6 is more important.
I understand the difference between NAT and firewall perfectly well. I have deployed and configured both for many years. The strawman of "NAT without firewall" is pretty much irrelevant, because that's not what people run IRL.
Firewalls are policy-based security, NAT is namespacing. In other fields, we consider namespacing an important security mechanism. If an attacker can't even name a resource they're not allowed to access, that's quite a strong security property. And of course, anyone can spoof IP and try to send traffic to 192.168.0.6 or whatever. But if you're anywhere in the world other than right inside my ISP's access network, you can't actually get the internet to route this to my local 192.68.0.6. On the other hand, an IPv6 firewall is one misconfigured rule away from giving anybody on the planet access.
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.
Thank you. This is the first time that someone admits here that NAT actually adds some security. IPv4 will never go away less that an important share because of it's simplicity and NAT-level security it offers to millions of professionals and amateurs that tinker with their routers.
NAT introduces complexity, not simplicity.
Besides, NAT isn't a security feature.
Secure and reliable IPv6 deployment has _more_ complexity than IPv4.
2 replies →
This is 100% correct, something the (dim) author of the article can't seem to understand.
Except in the real world everyone is also running UPnP, so NAT is also one misconfiguration away from exposing something publicly. In the real world your ISP might enable IPv6 one day and suddenly you do have a public address. Relying on NAT is a bad idea because it's less explicit, a firewall is saying you only want to allow these things through, of course nothing is perfect, you can mess up, but NAT is just less clear, the expectation is not "nothing behind NAT should ever be exposed", it's "we don't have enough addresses and need to share".
UPnP is not tied to NAT, where do you have this from? UPnP is used to request direct connections, a firewall can implement UPnP just as well as a NAT.
UPnP won't expose my SMB to the world on its own. For that you'd need an attacker already inside the NAT. So already on that side of the hatchway.
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It's not "relying on NAT" to have it as a layer in the swiss cheese. Relying on any one thing is a bad strategy.
Sure, and that's fine, but relying on it isn't, and it isn't a reason not to use IPv6 (if you want namespacing, there are tools for that outside hiding behind a single IPv4). Hence the advice is not to rely on NAT.
This is people talking past each other, and to be fair, saying "everyone" in my post made it unclear, I was being glib in response to "because that's not what people run IRL", when evidently people do, I've seen it happen.
No, not everyone is running UPnP. Maybe on most home networks, but that’s not the audience that even knows or cares about NAT.
I think this is where the disconnect is: the home users are precisely the ones being talked about, because they are the ones most likely to be treating NAT like it is a security system for their devices in the real world.
I've literally seen someone's ISP turn on IPv6, and then have their long-running VNC service compromised because they were just relying on NAT to hide their services.
> Except in the real world everyone
...and goes on to ignore enterprise businesses, which consume most of the v4 space and are among the biggest resisters of v6.
>Except in the real world everyone is also running UPnP
Definitely not. I've been disabling that for years.
Upnp on cgnat machines? Lol.
> It's sad how much of this thread of supposed hackers comes from people who are simply parroting this dogma because it has been drilled into them.
It's only been drilled into people because it's true:
* https://blog.ipspace.net/2011/12/is-nat-security-feature/
> If an attacker can't even name a resource they're not allowed to access, that's quite a strong security property.
This is entirely incorrect. An attacker can still name a resource, it only has to guess the right port number that is mapped to that resource.
That's how NAT fundamentally works after all, it allows you to use the additional 16-bits of the port number to extend the IP address space. Any blocking of incoming traffic on a port already mapped to a local address is a firewall rule.
The reason that it offers protection is because attackers aren't going to try every single port. Compared to that IPv6 will offer more protection as an attacker would have to guess the right address in a 64-bit namespace rather than just a 16-bit one.
That's absolutely not true, because forwarding rules don't exist by default. You can try all ports and will get no answer.