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DDoS Attacks Via DNS Recursion
Posted by
Zonk
on Thu Mar 16, 2006 01:37 PM
from the to-understand-recursion-you-must-understand-recursion dept.
from the to-understand-recursion-you-must-understand-recursion dept.
JehCt writes "Associated Press is running a story about how the recursion feature of open DNS servers can be used to launch massive distributed denial of service (DDoS) attacks: 'First detected late last year, the new attacks direct such massive amounts of spurious data against victim computers that even flagship technology companies could not cope.' A thread at WebmasterWorld explains, 'To make a long story short, having a DNS server that allows recursion for the Internet is like running an open SMTP relay.'"
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DDoS on Domain Registrar 69 comments
miller60 writes "Netcraft is reporting that 'domain registrar Joker.com says its nameservers have been hit with a massive DDoS attack, causing outages for customers. More than 550,000 domains are registered with Joker, meaning the outages could be widely felt. It's not clear why the DDoS is succeeding, as most registrars have implemented sturdy DDoS protection since the attack on the root nameserver system back in 2002.' Some security experts have warned in recent weeks about DNS recursion attacks as previously discussed here on Slashdot, which can amplify the power of attacks launched from botnets."
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djbdns (Score:3, Informative)
Re:djbdns (Score:5, Informative)
Parent
Fixing bind9 (Score:5, Informative)
Lets say that your local LAN and WLAN networks are 192.168.0/24 and 192.168.1/24, respectively. Make the following additions to your /etc/bind/named.conf.options (or equivalent):
Parent
Re:djbdns (Score:3, Informative)
You see, the chief difficulty is *exactly* the same as the open smtp relay problem. Back when everybody on the Internet knew each other, and abuse was resolved with a phone call, nobody understood that some services needed to be authorized, and some needed to be public. Thus, relaying and delivery SMTP servers were the same thing, and caching and authoritative DNS servers were the same thing
Re:djbdns (Score:4, Interesting)
Parent
Re:djbdns (Score:5, Funny)
Parent
Re:djbdns (Score:3, Insightful)
There was a server (named after a famous London landmark), which did DNS serving and also resolving, and was open to the whole internet (which, admittedly, wasn't too big). When customers moved away, they continued to use it for resolving. When the server was finally shut down in, errm, 1999 (wasn't the Y2k bug a marvellous excuse to get rid of services noone wanted to mai
Re:djbdns (Score:4, Informative)
It's very easy to define an external zone without recursion and some master zones and an internal zone that recurses. This also has the benfit of split caches. If you just disabled recursion for some clients in a "single-zone" BIND, you still are "vulnerable" to information leakage where external clients can probe your cache for records.
http://www.bind9.net/manual/bind/9.3.2/Bv9ARM.ch0
Parent
Separate authoritative and recursive (Score:4, Informative)
recursive, which is something that DJB has been preaching for a while.
Consequently djbdns won't do this, but it is quite possible to make bind not
do this also. (In fact Bind now has come round and reccomended this.)
It seems to me like a no-brainer, why is splitting the two such a problem?
SDNS wouldn't hurt either, but that will take a lot more doing.
Parent
Re:Separate authoritative and recursive (Score:3, Informative)
It isn't that hard, but it's perceived to be difficult. You have to set up your authoritative records on a separate IP address from your current DNS server (e.g. using tinydns). Then you tell your registrar that your nameserver has a different IP address. At that point, the only queries coming to your old IP address should be recursive queries coming from your users. Then you can close off recursive queries coming from the rest of the net (e.g. using dnscache).
The
That's by Berenstain? (Score:3, Insightful)
Besides, who wants software written by a cartoon bear?
Re:That's by Berenstain? (Score:3, Informative)
Wrong wrong wrong (Score:3, Informative)
No way is DJB software public domain.
In fact, I bet a dollar you don't even know what public domain is.
Re:Why do you think you need a license? (Score:3, Insightful)
Re:djbdns (Score:2)
Though if you're setting up a DNS server, you should have a fair amount of expertise on how those abuses can arise and limit the possibility.
Re:I love djbdns (Score:2)
Re:I love djbdns (Score:3, Interesting)
djbwm - it's the best window manager in the world, but when you try to move a window, it argues with you for ten minutes that it was already in the right place.
Re:djbdns (Score:3, Interesting)
Doctor, it hurts when I go like this (Score:3, Insightful)
OK, don't do that then.
Re:Doctor, it hurts when I go like this (Score:2)
"Don't do that, then" is not helpful advice to the people who are suffering from this attack.
Recursion == recursion == recursion == ... (Score:3, Funny)
See recursion [catb.org]. See also tail recursion [catb.org].
From the Jargon File [catb.org].
Could someone explain how the attack works? (Score:2, Interesting)
From what I understand of DNS resolvers, this attack can't work unless there's another compromise at play here. Either a compromise of one of the victim host's zones, or a compromise of the servers hosting the open resolvers themselves.
Re:Could someone explain how the attack works? (Score:5, Informative)
Parent
Re:Could someone explain how the attack works? (Score:5, Informative)
Another problem:
(Quoting a post on the other site)"they can send a 70 byte packet to your DNS server, and your DNS server will send a 500+ byte packet to the victim. With EDNS0, that can be 4,000+ bytes.
So with a dialup account, it would be possible to saturate a T1.
There's plenty of ways for them to mess with you without any 'compromised' machines on your network.
Parent
That's a bold statement (Score:3, Interesting)
Anyone want to discuss how DNS Cache [cr.yp.to] addresses this? AFAIK this is a pretty "safe" way to provide DNS to at least a small sized network - but that's all I run it on. Comments, concerns, advice?
Disable recursion in BIND (Score:5, Informative)
recursion no;
Problem solved.
Re:Disable recursion in BIND (Score:3, Informative)
Depending on the DNS server, turning off recursion completely is not the answer. Granted most internet-facing DNS servers can simply turn recursion off without negatively impacting lookups (generally) but doing so for an internal system (or one that bridges an internal and external) is begging for trouble.
According to Chapter 2.2.6.2 of Pro DNS and BIND ( http://www.zytrax.com/books/dns/ch2/index.html#re cursive) [zytrax.com])
overwhelming floods of amplified data (Score:2, Informative)
Suggestion:
-Verify requests
-Verify directory computers have not been comprimised
-Disallow amplified data
-Build a new secure system for handling traffic
There is a defense (Score:3, Funny)
/.ers will know that only the mighty foot of Chuck Norris [chucknorrisfacts.com] is powerful enough to kick back such a massive DDoS attack. There is a problem though: since there is only 1 of him, Chuck can't defend more than one site at a time. And ofcourse his ourly rates are a bit steep, too.
Vary your mileage may.Split-split DNS Design (Score:5, Informative)
ADVERTISER
RESOLVER
INTERNAL
The advertiser sits outside, Internet-facing, and is only responsible for resolving outside queries for your own domains. It does not do recursion or dynamic updates, and has a secured cache.
The resolver and internal sit inside, are intranet-facing, and handle internal requests for outside domains, and internal requests for internal domains respectively.
There are lots of articles on-line which show how to set this up.
Recursion considered harmful (Score:4, Funny)
old new (Score:3, Informative)
Re:old new (Score:3, Informative)
From outside your network, send a request for a DNS record to your server: a.example.com Your server will try to l
slashdot DNS is OPEN! (Score:4, Informative)
FAIL Open DNS servers ERROR: One or more of your nameservers reports that it is an open DNS server. This usually means that anyone in the world can query it for domains it is not authoritative for (it is possible that the DNS server advertises that it does recursive lookups when it does not, but that shouldn't happen). This can cause an excessive load on your DNS server. Also, it is strongly discouraged to have a DNS server be both authoritative for your domain and be recursive (even if it is not open), due to the potential for cache poisoning (with no recursion, there is no cache, and it is impossible to poison it). Also, the bad guys could use your DNS server as part of an attack, by forging their IP address. Problem record(s) are:
Server 66.35.250.12 reports that it will do recursive lookups. [test]
Server 12.152.184.136 reports that it will do recursive lookups. [test]
Server 12.152.184.135 reports that it will do recursive lookups. [test]
See this page for info on closing open DNS servers.
Re:slashdot DNS is OPEN! (Score:3, Funny)
Or maybe they read the actual article before posting it?
Sorry, just my little joke.
DDoS? "R", matey! (Score:3, Informative)
http://hyppy.zapto.org/DRDoS-Spyrochaete.html [zapto.org]
StormPay: A recent example of this attack (Score:3, Interesting)
As previous posters have noted, these attacks have become more frequent in recent months, prompting an advisory from US-CERT (PDF) [us-cert.gov] in December. It's a hot topic on several security lists, and a special focus of SecuriTeam blogger Gadi Evron [securiteam.com].
MOD REPLY TO PARENT UP (Score:3, Funny)
The real risk is perhaps The Final Virus [catb.org].
Re:I must resist (Score:5, Informative)
Parent
Re:I must resist (Score:3, Funny)
Re:I must resist (Score:3, Funny)
~S
Re:I must resist (Score:3, Informative)
Re:Old NEws (Score:5, Informative)
Parent
Of course there is... (Score:5, Informative)
Back in the bind 4 days, when I did serious DNS, my company wanted a few servers visible in their domain(s) for external dns host resolution.
For people behind the firewall, they wanted a far more extensive list of hosts that were not to be seen for queries outside the firewall.
I did this by using scp to transfer the zone files from the external to the internal DNS server; the internal server would then "cat" the additional hosts to the zone and HUP the named.
AFAIK modern BIND uses "zones" so you can accomplish the above on one server, if you want. I've never used it, but I can see a number of situations where I'd need my above solution even with this feature.
What BIND needs is not a "recursion no;" option, but instead a "recursion eth0;" or "recursion 1.2.3.*;" so recursive queries must originate from a trusted network.
Remember also that not everyone in the world uses BIND - people with ActiveDirectory or NDS name servers might be screwed until a vendor patch.
Parent
Re:Of course there is... (Score:3, Informative)
Re:Of course there is... (Score:3, Interesting)
The problem is doing the cache for internal hosts (or an internal interface) and running zone authority for external (internet) users on one server. Apparently it's not possible using the built in configuration tool. There's probably a registry key which determines which interface will forward or not, around here: HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\Cu rrentVersion\DNS Server
It
Re:When BIND is fixed I'll implement it (Score:5, Informative)
match-clients {
10.0.0.0/8;
};
recursion yes;
zone "example.com" {
yadda yadda yadda;
};
};
view "external" {
match-clients {
any;
};
recursion no;
zone "example.com" {
blah blah blah;
};
};
Parent
Re:When BIND is fixed I'll implement it (Score:3, Informative)
allow-recursion { localhost; mygroup; 10.10.10.1; 10.2.3.0/24; };
This would allow the localhost, the machines on the mygroup ACL, one computer at 10.10.10.1 and all the hosts in 10.2.3.0/24 access to recursive queries.
If you don't need to provide recursive lookups at all, you can just use this:
recursion no;
Re:When BIND is fixed I'll implement it (Score:4, Informative)
view "internal" {
match-clients { internals; guests; };
recursion yes;
zone "." {
type hint;
file "bootstrap/cache";
};
zone "example.com"{
type master;
file "example-int.com";
};
};
view "external" {
match-clients { any; };
recursion no;
additional-from-auth no;
additional-from-cache no;
zone "example.com"{
type master;
file "example-ext.com";
allow-query { any; };
};
};
---------
I believe that should prevent bind from being too useful from the outside.
Parent
Re:When BIND is fixed I'll implement it (Score:3, Interesting)
> turn it off ("additional-from-cache"):
Excellent. The commentary on the aite with the original article didn't seem to know about that trick. So now I just need to make sure I have wrapped my head around all of the details and start making the changes. Going to be a bit of bother this way but managable. Installing another pair of nameservers was right out, this way is doable.