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Comcast the Latest ISP To Try DNS Hijacking
A semi-anonymous reader writes "In the latest blow to DNS neutrality, Comcast is starting to redirect users to an ad-laden holding page when they try to connect to nonexistent domains. I have just received an email from them to that effect, tried it, and lo and behold, indeed there is the ugly DNS hijack page. The good news is that the opt-out is a more sensible registration based on cable modem MAC, rather than the deplorable 'cookie method' we just saw from Bell Canada. All you Comcast customers and friends of Comcast customers who want to get out of this, go here to opt out. Is there anything that can be done to stop (and reverse) this DNS breakage trend that the ISPs seem to be latching onto lately? Maybe the latest net neutrality bill will help." Update: 08/05 20:03 GMT by T : Here's a page from Comcast with (scant) details on the web-jacking program, which says that yesterday marked the national rollout.
You're IT for a business. You have employees who check their e-mail from home, accessing your stuff via a split tunnel VPN.
The computer tries to resolve internalmail.company.com, and normally this should fail, causing the computer to try the VPN's DNS server.
Instead, your employee's computer gets Comcast's search page server. Their mail client times out.
You get inundated with tech support calls.
Which, if true, makes the opt-out process even more ludicrous. If I'm at home opting out, shouldn't they just DETECT my mac address, and do the opt-out automatically?
Instead, I had to enter my mac address manually (along with my e-mail address) - and then they told me it would take two business days to go through. (Granted, I got a confirmation e-mail the next day saying it was done, but why isn't this automated?)
I've always used a linux box as my firewall /router box at home, and I've been running BIND as a caching DNS server. Fortunately this won't affect me, as I totally bypass spamcast's bullshit.
Lawyers, MBA's, RIAA? A jedi fears not these things!
My ISP does this. They also have an 'opt-out' option, but you know what that does? It still doesn't send an NXDOMAIN response like it should. Instead it redirects me to a site that is serving the standard windows site-not-found page. A horrifying experience for this mac/linux user.
So I set up my own DNS server, which fixed the problem and sped up my internet connection since the ISP's DNS server was really slow.
It's a split tunnel VPN...
That means first it tries to use the internet, then it tries the VPN. If I lookup foo.bar, and foo.bar doesn't resolve, it then tries on the VPN's DNS. That helps keep external traffic off the VPN. Internal traffic is still safe.
Of course, if foo.bar instead of not resolving--points to comcast--then I never do the lookup...and the VPN ...is broken.
To use an example from my company, we have many users with laptops. We have set up MS Outlook on these systems to use Outlook Anywhere. The way Outlook Anywhere works is that is first tries to connect to the internal mail server (mail.company.inside) and if it can't connect to that then tries the external mail sever for an Outlook Anywhere connection (mail.company.com). With a properly set up and unmunged DNS, when they are at home it tries to connect to the internal server and gets a DNS not found response and then tries the external server. With this new bothced DNS setup, it tries the internal server and gets an IP address response, so it tries to connect to that server to retrieve it's email. Unfortunately, the DNS sends the IP address of the web server that serves up it's ad page, so Outlook sits and times out waiting for a response, meaning these people can't get their email from home.
Yes, this could be worked around by host files, but we are 1000 person company. Why would we want to try setting up local host files on these systems that then have to be updated whenever we change servers just because an ISP doesn't want to set up DNS based on the proper specs?
"Information wants to be expensive" - Stewart Brand, the same guy who said "Information wants to be free"
The name of the box is, of course, irrelevant. But you still have it wrong: Comcast's DNS server isn't affecting the company's internal DNS server, it is affecting their customer's box, who is your employee, making it so that they never query your internal DNS server.
This happens precisely because they don't know anything about the internal network, and yet they are telling your employee they do.
'Sensible' is a curse word.
So if you are trying to pen test some machines you own and Comcast points you to their server who is to blame? Are you really responsible if Comcast hijacks your DNS requests and sends you to their server?
I was testing against a known invalid DNS entry (ie: personally owned but not parked domain name). How are you responsible when they hijack your connection?
Even better is when someone pwns Comcast's server and and exploits all of Comcast's customers with a browser exploit hosted there.
I fail to see, using your scenario, why Comcast's DNS server would effect the company's internal DNS server, thus creating the conflict you alluded to. Since I'm not sure why Comcast would know anything about the company's internal network...
That's because you didn't pay attention to the scenario. We're talking about a split tunnel VPN. DNS resolution uses the following rules:
1) try the usual (external) DNS server first. If it resolves, use that IP address for the communication.
2) try the internal DNS (via the VPN) if step 1 returned NXDOMAIN, and if that resolves, use that IP address for the communication.
3) otherwise, return NXDOMAIN.
So if Comcast's external server returns a valid IP for the internal server, instead of NXDOMAIN, then your internal mail server will never be accessible to anyone using your company's VPN from a Comcast connection.
DNS is supposed to tell you (essentially) "no such domain name registered" when you try to find a domain name.
IFF (e.g. if and only if) DNS _only_ serviced web browsers, then one noise-page (my adverts here) is no different than any other noise page (no such name) because a human is going to go "oh, that's not what I was looking for".
But there is a heck of a lot more going on out here in the internet than just web browsing, and significant portions of it hinge on getting true and correct answers from the DNS system.
With DNS boned-up to return false positives on all names, then money can be stolen from you, the causal web browser. For instance, I send you an email from support@bankofamercia.com; you don't notice the transposition of letters, your spam filter looks up bankofamercia.com and the DNS service return as IP address instead of no such address, that address is the same one as I spoofed in the email, the spam filter says its a good email, you get owned.
Okay, that _is_ contrived, so try this instead...
It's 1964. You are at a pay phone. Your car has broken down. It's your last dime. You call home, but mis-dial a number that doesn't exist and you get a busy signal, and you get your dime back. You call home again and get help. The system worked.
It's 1964. You are at a pay phone. Your car is broken down. It's your last dime. You call home, but mis-dial a number that doesn't exist and some random person answers and proceeds to try to sell you car wax. Your dime is gone. You are still stuck. The system has failed.
Imagine your life if you _never_ got a busy signal. You call any extension in any company and you get to leave a voice mail but nobody will ever get that message. It would be living hell.
Worse yet, you run a small company, you may a small number of sales each month that are vital to your companies survival. You invest in an expensive advertisement on the superbowl and everything goes great. Then your DNS server dies. Now there is nobody to answer the proper DNS queries. The DNS squatter wakes up and since mylittlecompany.com no longer resolves, all that traffic goes to the Comcast Advertisement Shill page. In just a few minutes you get your DNS server working again, but everyone who got the bogus page thinks your company is trying to sell comcast telephone service and web search services and you never go that business. You are out big cash and your name is ruined. IF the spamvertisement page hadn't been there, those people might instead be thinking "wow, this service is so popular I cannot get in, maybe I'll try back in a bit" instead of "why did comcast decide to take out a superbowl ad that made it look like they sold that interesting little product?"
In short, what if every time your cell phone couldn't be found (because it was off or the battery died etc) the people trying to call you got silently redirected to a random "service" of the type one sees on late night television, offering jokes or sex chat, ostensibly in your good name?
That's what is wrong with doing that.
Innocent people shouldn't be forced to pay for inferior software development.
--"Code Complete" Microsoft Press
Using DNS lookups to tarpit certain kinds of spam. If everything resolves, then such methods simply fail.
Besides, interfering with DNS resolution is just plain bad. Quite frankly, I wish we had an organization controlling the root servers that had a backbone, and would simply stop answering queries from any network that decided to interfere with DNS resolution.
The world's burning. Moped Jesus spotted on I50. Details at 11.
http://tools.ietf.org/html/draft-livingood-dns-redirect-00
note where author works.
Your opt-out request has been confirmed. We will complete processing of this request within 2 business days.
I wonder if /.ing the Comcast request page makes it take longer. ;-)
HOLY FUCKING SHIT
STOP SUGGESTING OPENDNS, THEY DO THIS SHIT TOO.
Excuse my while I go blow a bloodvessel. Every single time a story like this comes up some idiot suggests OpenDNS and idiot mods initially mod them up.
I'd link where this happened last time but for the life of me I can't figure out how to view more than my several dozen posts.
"linux is just DOS with a UNIX like syntax" -- Galactic Dominator (944134)
Because after all, if I don't use their DNS, why should I care where they are directing non-existant domain traffic to?
Using OpenDNS, Treewalk, ns1.sprintlink.net, etc doesn't matter because a) Returning the A record when the domain does not exist blatantly violates the RFCs: the established commonly agreed upon standards without which the internet would cease to function and b) some ISPs redirect your DNS traffic to their servers whether you like it or not. Some outright block DNS servers that don't belong to them, and others silently redirect your requests. c) In the README file of your latest application, you shouldn't have to tell everyone that they need to use your DNS servers just to get a *correct* response.
It isn't just you at home with your pr0n that has to deal with this BS. I have to deal with it where I work, because my company's ISP is a cable provider who does this redirect crap. So when I go to write an app that *might* use DNS, I have to screw with this nonsense because the cableco can't be bothered to return an NX - but instead always returns an A record for their server - subject to change without notification. So when they change to redirect to another server, wtf am I supposed to do then? The only way my app could possibly tell there was a problem is to see if the response matches this redirect server. And no, it isn't an option for my application to just willy nilly pick a DNS server of its choice to use. My application requests a lookup from the OS's network layer, but has no particular knowledge of the DNS servers - exactly how it is supposed to be.
If I give my app to other people, are they supposed to put into the app's configuration the A record information that would correspond to their particular ISP's "redirect" host? My app needs to know when the DNS lookup failed. I have no way to tell when every damn name returns an A record. I count on the DNS server to respond in the way the RFCs set out. Comcast and the other ISPs are saying "fuck your rules"
As has been said until we're blue in the face:The internet is not the web. If the ISPs and the browser folks want to sit down and see what the RFC permits and figure out how to return a url in the NX that the browser would recognize and could handle, then I have no problem with that. As long as it doesn't interfere with the normal operation of an NX response. As I'm sitting here thinking about it, the place for this information seems to be either in the DHCP lease, or in the wpad.dat auto-proxy configuration file. But Comcast and the others like them have decided they don't have to play well with others.
There is very little future in being right when your boss is wrong.
Comcast's version is an order of magnitude better than everybody else's.
a: There is a REAL opt-out, that puts your DHCP lease to point to a DNS resolver that doesn't do this. I'll have to do this when I get home. Compare this with, eg, Verizon's pitiful opt-out instructions involving manually changing DNS settings.
b: IF you had manually set your DNS resolver to a Comcast server, you are unaffected (they added new resolver addresses to do this), per previous discussions by the Comcast folks over at Broadband Reports.
c: It does NOT get *.whatever, only www.*.(TLD), thus even when you don't opt out, it is at least limited to web-related typos. This is actually a big deal, as I think Comcast is the first one NOT to do it for everything.
I don't like NXDOMAIN wildcarding (it was one of the motivations behind building the ICSI Netalyzr), but if an ISP is going to do it, Comcast's is actually well constructed to both limit collateral damage (it only gets www.*) and be able to be bypassed with a real opt-out.
Test your net with Netalyzr
DNS hijacking isn't evil because the companies that do it is evil. It's evil because it breaks standards, and therefore breaks all sorts of other crap.
It doesn't matter what company does it, it's still fucked up. To suggest that OpenDNS breaking standards is any better than Comcast breaking standards is just plain stupid and clearly missing the point entirely.
"linux is just DOS with a UNIX like syntax" -- Galactic Dominator (944134)
The other side of the coin is the customer experience. Think about the average internet user. They cannot tell the difference between a 404 error and a 504 error.
People often unknowingly mistype URLs and automatically believe that their internet is broken and they need to call their ISP in order to get it working again. My personal experience working tech support for a large ISP is that mistyping domain names is a huge call driver, and this service is meant to address that.
That's the other side, now flame on.
My comments here are my own; I do not speak for my employer.
Look at the DomainHelperLogic and the only thing it hijacks are DNS lookups that begin with www and end with a valid TLD (.com, a ccTLD like .us, etc.).
While I think this still stinks that they are hijacking DNS at all, and as a Comcast customer I will complain and opt-out, I think they're doing it in a fairly logical way.
But it's not that bad. If you do a DNS lookup for any domain (say for an MX or NS record) you're never going to see this. Your lookups will only be affected if the query starts with www, followed by a domain, ending with a valid TLD (.com, a CC, etc.).
If your internal office uses something such as mycompany.internal, then even a www.mycompany.internal query isn't going to get hijacked since .internal isn't a valid TLD. If you are using mycompany.com for internal use, you should own mycompany.com externally, and negative replies will still work and not get hijacked.
Again, while I oppose monkeying with DNS, this appears to be fairly well thought out and not anywhere near as bad as most other implementations.
We're talking about the DNS search, not actual routing. First you check the internet and then you search the VPN DNS. This is so that if $work is doing the same type of redirection (which is fine - it's their resources that they're serving, so if they don't want you going to playboy.com, that's their business) you can still reach the external network without using $work's resources. There's no reason why your employer's computer-use policies should interact with your home use, even when connected to the office over VPN.
This requires that your DNS is resolved via the internet before VPN. And requires that the internet DNS behaves properly.