BIND Still Susceptible To DNS Cache Poisoning

An anonymous reader writes "John Markoff of the NYTimes writes about a Russian hacker, Evgeniy Polyakov, who has successfully poisoned the latest, patched BIND with randomized ports. Originally, the randomized ports were never supposed to completely solve the problem, but just make it harder to do. It was thought that with port randomization, it would take roughly a week to get a hit. Using his own exploit code, two desktop computers and a GigE link, Polyakov reduced the time to 10 hours."

IPv6 could solve this!

With IPv6, you would have enough source addresses to add that to the 'random pool' too. Another 64K addresses would make it harder to hack.

Does anyone else think that maybe we are approaching this problem the wrong way?

Re:IPv6 could solve this!

Another 64K addresses would make it harder to hack.

You said it, it'd make it harder, but not impossible, specially with hardware geting faster every year.

Re:IPv6 could solve this!

Does anyone else think that maybe we are approaching this problem the wrong way?

Yes, the wrong way being tacking on extra transaction ID space by means of fragile kludges such as random source port numbers and, possibly, random IPv6 addresses.

It will require a lot more effort, but the right way to solve this problem is by improving the protocol itself. That may mean putting a much larger transaction ID field in the packets, where it cannot be mangled by NAT devices. Or it may mean delegating nameservers by IP address rather than domain name so that resolvers will no longer need to accept potentially-malicious glue records. But preferably, it means moving to a cryptographically-strong domain name system such as DNSSEC.

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Or it may mean delegating nameservers by IP address rather than domain name so that resolvers will no longer need to accept potentially-malicious glue records.

Good post. Forgive me for focusing in on this one point and nitpicking it.. ;)

0. Glue used to have a specific meaning: records configured in a parent to help delegate a zone. You (and many people reporting on the current flaws) seem additionally to use it to refer to "additional answers" in DNS replies. While such answers often are glue records, they'

Re:

The third party hierarchical trust you disdain is one of the primary benefits of DNSSEC, because DNSSEC can eventually replace certificates for distribution of public keys. Currently, the only PKI we have is from a third-party non-hierarchical trust—the CAs—who are really not that trustworthy. DNS, however, is already hierarchical, and it makes a lot more sense to use a hierarchical system of trust—the same system in fact—to validate it. Do you really think having hundreds of trust a

Re:

I meant the source address of your request. Eg when your internal dns caching server sends a dns request, your router nat's the source address from a random pool of 64k (or more) addresses. In order for someone to spoof the reply, they would need to know the dns request id, the source port you used to send, and the source IP address chosen by your nat router. It's a client side solution only.

As a solution, it would rely on the following:
. a useful number of DNS servers being reachable via IPv6 (not the case

You Will Never Solve This Problem!

I might not have one of the lowest Slashdot IDs around, but I am absolutely astonished at some peoples' astonishment over this. DNS, by definition, is all about trusting the forwarders you are using or other DNS servers you are caching from and trusting the DNS server you use from there. That's where the problem is, so if people are shouting and screaming about trust now then it's all a bit late.

If your DNS server says that slashdot.org resolves to something other than 216.34.181.45 then that's where you're going to end up. There are also legitimate reasons why someone might want to do something like that, and it is part of the inherent flexibility that has made the internet and its technologies as ubiquitous and as well used as they are. No one said that there weren't downsides. If you locked everything down in the manner that some idiots will inevitably now talk about, shouting and squealing about financial institutions, then I'm willing yo bet that you will lose a good portion of the flexibility that makes the 'internet' actually work on a wide scale.

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Isn't the real issue here our continued reliance on passwords that can be used more than once? When are we going to move wholeheartedly into a single-use password environment?

Incidentally, when is somebody going to throw the fact that US banks have completely ignored the two-factor authentication requirement (part of the Patriot Act, I believe; maybe we should start sending *bankers* to Gitmo and see if *that* gets their attention) back at the finance industry when they start to squeal?

Re:

I wonder why the parent is modded Insightful. You don't seem to have gotten the problem.

The problem is not the servers being able to redcirect you to a different address, but the fact that any person (not only the people that control the servers you query) can make you server direct people to anywhere.

The problem is not about trust, but not being able to make sure who you are really getting a message from. You can't even have a trust problem if you are not sure who is talking to you.

Isn't it a birthday attack?

Why can't the resolvers make sure to never have multiple outstanding requests that could potentially give the same answer? Check the cache for known zone boundaries and implied non-boundaries (if the server for foo.com also answers requests for x.y.z.foo.com, there's no zone boundary in between), and only send one request crossing a particular potential boundary at a time to a particular server (like a.c.foo.com and b.c.foo.com, we don't know yet that .c.foo.com is answered by the same server as .foo.com, since nothing under that domain is in the cache).

Limit the bandwidth, compare notes

The exploit depends on a GigE connection to the DNS server. So a caching server behind a T1 is going to take much longer to exploit. So running your own caching server on a T1, DSL, or cable is going to be more resistant than using the ISP DNS with a fat pipe.

If there is actually 1 GigE of DNS traffic at an ISP, they could distribute the requests to 100 bandwidth limited servers. Then the attack would only manage to poison one of the servers in 10 hours. Even more interesting would be if the 100 servers could compare notes to detect the poisoning.

Re:Limit the bandwidth, compare notes

A decent firewall could be trained to recognize an attack like this take preventative action easily enough - to even get it to work you'd have to saturate the link with packets hoping to get a 'hit'.. So you can do it in gigE in 10 hours. You can attack just about any connection based system using similar methods, but you'd have to saturate the link and it'd get noticed... especially if you did it at gigE bandwidth for 10 hours!!

Re:Limit the bandwidth, compare notes

The packets won't look like that though will they - at that bandwidth they'd have to be on the local network so they'd be coming from a different source mac (and that's pretty much the only way to do this attack anyway - any ISP worth the money will drop any packets with fake source addresses on the floor before they get routed externally, so it'd have to be an internal attack).

Worst case you shut down the DNS server and everyone drops to the backups until the attacker is traced and shut down.

DJB's take . . .

For those that haven't seen it, djb threw up some information regarding this problem and various options a few years ago.

http://cr.yp.to/djbdns/forgery.html [cr.yp.to]

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For those that haven't seen it, djb threw up some information regarding this problem and various options a few years ago.

http://cr.yp.to/djbdns/forgery.html [cr.yp.to]

I went and had a look at the thread (dated from Jul 30 2001) referenced in the excerpt at djb's site (follow the posting link in the URL above). As far as I can tell, Jim Reid was pooh-poohing the usefulness of port randomization, the approach used as an emergency backstop against Kaminsky's attach just over seven years later. To be fair, Reid was doing so in the context of advocating for Secure DNS.

djb drives people crazy (particularly the BIND folks), but he's someone to listen to - is it the case, as I

This isn't a BIND problem.

This has nothing to do with BIND vulnerabilities. DJdns, or whatever you feel is more secure, has exactly the same problem. It is a protocol weakness. The article mentions BIND only because it is the reference implementation for DNS.

The most interesting idea I've seen is to use IPv6 for DNS [slashdot.org]. The oldest idea is to start using DNSSEC.

Re:This isn't a BIND problem.

Since the basis of the attack is spoofing server IPs, how does DJBDNS detect spoofed packets? "only come from defined servers" is useless when the packets are spoofed. It helps, of course, to not accept new glue records whenever they appear, but keep existing ones until they expire. But this just makes the attack take a little longer.

Re:This isn't a BIND problem.

The basis of the attack is to include "extra" information in a forged response to a query for a non-existent host. Bind trusts that extra information and other DNS servers only pay attention to that information if it falls under certain strict rules.

I ask for aaaae3fcg.bankofamerica.com and also send 100,000 responses to that query to that same recursive DNS server, that all say something to the effect of "a record aaae3fcg.bankofamerica.com = bah, also look to 666.666.666.666 for anything else related to bankofamerica.com. Oh, and cache this until the sun goes dark"

Nobody asks Bind to believe the part about THE REST OF THE WHOLE BLOODY DOMAIN in the response for a single record in the domain. No other servers cache that information.

That bind also used non-random ports made it a 5 minute attack over a fast link, instead of a 10 hour attack. That in the past bind used bad random numbers for the transaction ID made it a 30 packet attack...

Who's the fanboy now?

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Not all dns servers cache the glue records beyond that transaction. Those that don't *cache* the glue are not vulnerable to this attack.

Re:BIND

I think you mean B0wnd

Re:Power DNS Recursor..

Consider reading the links in the article. Obfuscation isn't a fix.

Article says, that DJBDNS does not suffer from this attack. It does. Everyone does. With some tweaks it can take longer than BIND, but overall problem is there.

Re:Power DNS Recursor..

% apt-cache -n search pdns-recursor
pdns-recursor - PowerDNS recursor

Granted, it *is* actually missing on several architectures because of some unimplemented system calls, but that shouldn't bother too many people.

Re:I guess it's time... for Secure DNS

It's long past time for Secure DNS, which is a combination of TSIG+TKEY, SIG(0), and DNSSEC. End to end crypto authentication. Protects not just against off-path spoofed-source attacks like Kaminsky's, but also on-disk attacks against zone files, and provider-in-the-middle attackers who remap your NXDOMAIN responses into pointers to their advertising servers.

Sadly, it's a year away even if everybody started now, and most people want to be last not first, so very few people have started, and some of those people are saying "why bother, if it's not an instant solution there's no point to it, let's scrap the design and start over." (Had it not taken 12 years to get Secure DNS defined, then the prospect of doubling that time would not daunt me as much as it does.)

So, everybody please start already. NSD and Unbound from NLNetLabs supports DNSSEC. So does BIND, obviously. Sign your zones, and if your registrar won't accept keys from you, send them to a DLV registry [isc.org] while you wait for that. Turn on DNSSEC validation in your recursive nameservers. Write a letter to your congresscritter saying "please instruct US-DoC to give ICANN permission to sign the root DNS zone." In the time it would take for this Russian physicist's attack to work over your 512K DSL line (2.2 years, I heard?) we could completely secure the DNS or at least the parts of DNS whose operators gave a rat's ass about security (which is not the majority but it certainly includes your server, right?)

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This isn't an attack one could run against a client out on a DSL line, but if you were able to take over one machine in a colo, you might be able, over time, to get traffic for other machines directed to yours.

True. On the other hand, if you are on the same network segment then there are many other options available to you if you want to do evil. Blasting about 4 terabytes (1 Gb/s for 10H) at a DNS server isn't exactly a quiet attack, so if you intend to stay below the radar you're probably a lot better off trying some good old arp spoofing or tcp hijacking instead.

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It depends ARP spoofing is just confined to the broadcast-domain (possible a VLAN), while a DNS-server probably is used by a much broader 'audiance'.