Kaminsky's DNS Attack Disclosed, Then Pulled

An anonymous reader writes "Reverse engineering expert Halver Flake has recently mused on Dan Kaminsky's DNS vulnerability. Apparently his musings were close enough to the mark to cause one of the Matasano team, who apparently already knew of the attack, to publish the details on the Matasano blog in a post entitled 'Reliable DNS Forgery in 2008.' The blog post has since been pulled, but evidence of it exists on Google and elsewhere. It appears only a matter of time now before the full details leak." Reader Time out contributes a link to coverage on ZDNet as well.

Comments

The push for DNSSec

[QuantumG]

Kinda makes you wonder what they're getting out of it.

Re:The push for DNSSec

[mrsbrisby]

Paul is an idiot and a douchebag. He's been lying to you for a long time to cover his own ass: BGP routes are filtered everywhere which means that not only do you have to break the port, and the sequence number, you also have to break the route filtering every AS is already doing.

Meanwhile, had BIND simply gone and removed the stupid ADDITIONAL-section processing like DJBDNS did, you wouldn't be having the described vulnerability.

Re:The push for DNSSec

[0xygen]

Not to be paranoid, but the argument of "no-one can do this" is often weak in the light of it being governments or intelligence agencies who are trying to mess with your internet access.

Is he scared of his government?

Or concerned about what his government may be doing to others in the world?

The problem is not necessarily on the "some attacker half way across the world on another AS", but may be much closer to home.

Re:The push for DNSSec

[mrsbrisby]

To be blunt, "the government" can crack your DNSSEC keys as well.

LAN security doesn't enter into it- if your cache is on the same machine, and you're using switched ethernet to the border, any remaining attack vectors "close to home" remain on the same level as transparent proxies and whatnot.

Where is your god then?

You can play with the search query

[mysidia]

Use Google search snippets to expose little details of the document...

I'm guessing some persistent folks will eventually be able to piece the bits together.

i.e. see how much you can piece together from the summary with the result shown by google. Adjust your search by including unique words towards the end of the snippet in one search to try to get the text that follows.

1

2

21 Jul 2008 ... One of them involves mucking about with the QID in DNS packets and the ... The QID is the only thing protecting the DNS from Mallory (me). ...

21 Jul 2008 ... If Mallory wins, the next 10000 or so people that ask that cache where WWW.VICTIM.COM is go to 6.6.6.0. 3. Then thereâ(TM)s that other set of ... 21 Jul 2008 ... Then thereâ(TM)s that other set of DNS vulnerabilities. ... Then letâ(TM)s set up an evil server with it, and register it as EVIL.COM. ...

21 Jul 2008 ... EVIL.COM, and watch how the QIDs bounce around; eventually, sheâ(TM)ll break the .... EVIL.COM and slipping strychnine into his ham sandwich, ...

21 Jul 2008 ... This will be Bobâ(TM)s unique identifier for his sandwich acquisition transaction. Note that the number will probably be used twice â" once when ...

21 Jul 2008 ... Which sends back a response with an unexpected (evil) Additional RR. ... Weâ(TM)ll come back to it. Alice has an advantage in the race, ...

21 Jul 2008 ... Alice has an advantage in the race, and so she likely beats Mallory. NXDOMAIN for AAAAA.VICTIM.COM. Aliceâ(TM)s advantage is not insurmountable. ...

21 Jul 2008 ... Aliceâ(TM)s advantage is not insurmountable. Mallory repeats with AAAAB.VICTIM.COM. Then AAAAC.VICTIM.COM. And so on. ..

21 Jul 2008 ... Frequently, that server has to go ask another, and so on. .... And so on. Sometime, perhaps around CXOPQ.VICTIM.COM, Mallory wins! ...

21 Jul 2008 ... If Mallory wins, the next 10000 or so people that ask that cache where WWW .... COM, Mallory wins! Bob believes CXOPQ.VICTIM.COM is 6.6.6.0! ...

21 Jul 2008 ... Poisoning CXOPQ.VICTIM.COM is not super valuable to Mallory. ... Because her response didnâ(TM)t just say CXOPQ.VICTIM.COM was 6.6.6.0. ...

21 Jul 2008 ... COM was: 6.6.6.0. Every resolver that points to that name server will now ... COM to 6.6.6.0. Those records are in-bailiwick: Bob is in fact ...

I thought this wasn't the X attack from Y..

[dnsfool]

If this is the real deal, there's some bogosity here. This is certainly not a new attack or flaw in the dns protocol, any more than run of the mill dns cache poisoning is. Spoofing responses from the root servers (to hijack a TLD) is difficult; their TTLs are long, there are many of them (more unpredictability), and most DNS servers service so many requests that it's unlikely that your spoofed answer will be the first one to hit the server and thus poison the cache once the TTL for that TLD has expired. Spoofing responses from TLD servers is standard issue cache poisoning, and you cannot use it (any more) to poison a cache with an irrelevant record; BIND is going to ignore any NS, A, SOA, or other records for bankofamerica.com. in the additional or authoritative sections if the request was for some-domain-that-don't-exist.com. I'm back to where I was before; not seeing anything new here except a clever theoretical attack that would work much better if the TTLs for the TLD servers were on the order of minutes or hours rather than days. Either Halver guessed wrong, or the security community has been mislead about the severity of the issue.

Re:I thought this wasn't the X attack from Y..

[dnsfool]

Yes that's the right idea, but it seems that just changing this concept of a "balliwick" would solve the issue.

There's no legitimate need for your bogus "www.bankofamerica.com" RR to be accepted when you're asking about "xxffgg.bankofamerica.com."

It makes sense to accept it when you're simply asking about "bankofamerica.com"; that's how normal glue works, but you already have the information you need regarding the domain itself, so accepting more unsolicited information doesn't provide you with anything.

Servers only need glue when they're traversing the chain. Once they're at the level they need to be at, they should ignore any other records (glue or otherwise) that are sent.

Use djbdns (aka tinydns)

[Neanderthal Ninny]

Use djbdns which is immune to this attack. Dan Bernstein actually described this in 2002 http://cr.yp.to/djbdns/res-disaster.html

djbdns is not prefect but has been better than BIND which had it large share of bugs and security problems.

It's okay...

[davidu]

There will be more (new) announcements in the coming week or two. The DNS is gonna be fun for a while, unfortunately. We prefer it to be reliable and accurate.

Even worse...

[AySz88]

According to the "confirmed" post by Thomas Dullien aka Halvar Flake (found via this PCWorld article), the problem might be even simpler than that. He issues requests for some non-existent domain in .com, instead of a non-existent subdomain in the domain you're attacking. Can anyone confirm, or must it be subdomains?

Subject lines tell me how to mod

[KWTm]

Frankly, we should just do away with the subject line entirely. They generally just get filled with "Re:Re:Re:Re:Unoriginal First comment" anyways. It serves no purpose in a system like slashdot's, and causes things like the above.

Interesting you say that. Whenever I get mod points, the subject line is one of the things I look at to see where to grant my mod points.

Reading every posting to see which ones are worth modding up would be too much work. I look for replies in a thread where the author has taken the effort to change the subject line from "Re:Re:Re:Re:Unoriginal First comment" to something relevant; these have a much higher chance of being insightful or interesting. The more concise and pithy the subject, the more I make sure I click on it to read; a subject line like "Not true: ABC is counterexample" conveys more information than "You're wrong!" and is correspondingly more likely to be modded up.

I'm not saying that a catchy subject line is enough to get mod points from me, but those are the ones I will read first.

Okay quick question.

[ledow]

Okay, I don't dabble deep in DNS but I have a few quick questions. The RR thing is nasty because sub-domain authority implies domain authority. That's just silly and I'm stunned that something so simple is still true. I imagine there are a million and one "good" reasons for it, but it appears to be a gaping hole that could easily have been removed.

However, on the "let's spoof a DNS response" front - if a DNS server/client is being sent lots of spoof reponses, how long until they are picked up by a filter and blacklisted, tarpit'd or similar at the ISP end? This is the solution surely, even if you can send millions of packets with incorrect QID's and similar identifiers at a DNS server, like any other service at some point it has to say "you're trying to be naughty" and blacklist any packets, sound an alert, get the upstream filters to block such traffic etc. (This is, of course, assuming that there are at least some systems in place to stop or limit source-IP forgery in the first place). It might even be a good idea, at this point, for such servers to not trust their data, and constantly compare their copies with those available from the nameservers. If "fluctuation" of the data (between real and spoofed responses) is detected, then sound an alert on that domain.

How many responses does an average DNS server get that are invalid because of purely accidental causes (e.g. corrupted packets, mis-configured routers etc.)? Surely it's so few that it can instantly blacklist any suspicious activity, like trying to poison recursive caches in this manner.

I imagine that most home routers are extremely stupid and can't stop such things because they rely almost exclusively on the ISP's DNS servers to do their job and a flood of fake packets will not be picked up (this is, however, one of the reasons that I've always used "DMZ" or PPP half-bridge settings on ADSL routers to throw all external packets towards a real server rather than relying on some VxWorks firmware to handle IP-based attacks). But the servers? They *should* be filtering, cleansing and blacklisting packets even before you get into whether they have the most up-to-date patches, and a security fix to enhance the randomness of X etc.

It seems that the DNS servers are too trusting of "correct" packets that come as part of packet-floods of incoming data that is *obviously* false. DNS clients accepting data appearing to come from a trusted host is not nice, I agree, but recursive DNS servers should know better.

Or have I missed something incredibly obvious here?

I don't really care because my ISP wasn't vulnerable to this attack when I first tested it about 10 minutes after the first posting about its potential on the blog, and I'm pretty sure that they wouldn't have had any more advanced warning than anyone else.

Having said that, the DNS servers provided by LGfL's broadband supplier are, apparently, vulnerable. (London Grid for Learning, a London-wide schools extranet that virtually every London school, of which there are hundreds, use for their Internet connection, DNS servers, content filtering, etc. as well as their external content host). But, knowing LGfL and the way UK IT operations that are in any way involved with government work, that's not surprising at all.

Re:Here's the whole post

[AftanGustur]

Here is why it works (I think):

Malory wants to poison the server ns.polya.com

Malory sends NS requests for ulam00001.com, ulam00002.com ... to ns.polya.com.

Malory then sends a forged answer from the .com server, saying that the NS for www.ulam00002.com is ns.google.com *AND* puts a glue record saying that ns.google.com is 66.6.6.6

Because the glue records corresponds with the answer record, (same domain) the targetted nameserver will cache or replace it's curent record of ns.google.com to be 66.6.6.6

Hmmm, can't be that simple, can it ?