By Kelly Jackson Higgins
February 11, 2008
The industry is just one multi-million-dollar corporate data breach away
from waking up to the serious and often-silent threat of corrupted DNS
resolution servers, says DNS inventor Paul Mockapetris.
Mockapetris -- who is also chief scientist and chairman of the board for
network naming and address vendor Nominum -- says the recent research on
corrupted DNS resolution servers by researchers at Georgia Tech and
Google demonstrates yet another way the bad guys are attacking DNS to
infect users. (See Hacking a New DNS Attack .)
Researchers David Dagon, Chris Lee, and Wenke Lee of Georgia Tech, and
Google's Niels Provos, dubbed the new threat "DNS resolution path
corruption, where malicious DNS servers provide false information in
order to send users to malicious sites. The researchers officially
presented their findings today at the Network and Distributed System
Security Symposium (NDSS) in San Diego .
In their study of DNS resolution, they found around 17 million
open-recursive DNS servers on the Net, and discovered that about .4
percent, or 68,000 of them, are performing malicious operations by
answering DNS queries with false information that sends them to
malicious sites. About 2 percent are returning suspicious results, they
This report demonstrates that people are getting lured out to dark
alleyways of the Internet. The actual damage isnt documented here, but
it will be somewhere when someone loses the first $10 million to $100
million to this type of attack, Mockapetris says.
This growing method of attack forces users to rely on rogue DNS servers,
which results in what the researchers call a second secret authority on
the Internet. They found dozens of viruses that infect DNS resolution
paths, and that hundreds of URLs each week do drive-by alterations of
host DNS settings.
There are obviously legitimate reasons for redirecting or editing a DNS
entry/registry, such as with organizations like OpenDNS that block
unwanted sites and correct fat-fingering mistakes from sending a user to
a typo-squatter's site. But users need to be aware that the bad guys
have also figured out how to abuse DNS this way, Mockapetris says.
So a user working off a public WiFi port, for example, is at the mercy
of the DNS servers it uses, which "could easily be malicious," he says.
The Georgia Tech and Google researchers focused on malicious alteration
of DNS answers in their study. Companies are rewriting DNS answers,
ideally to improve the user experience, but also to expose the users to
ads, says Georgia Techs Dagon. There are also some laudable security
improvements that come from rewriting answers. For example, OpenDNS can
protect users from malicious sites. But DNS vendors aren't the only ones
commercializing the alteration of DNS traffic. Malware authors also use
this technique to exploit victims.
Nominums Mockapetris says combating this threat may require revisiting
the DNS food chain -- meaning data from the user who owns the domain, to
the user who wants to access it, and who gets to modify it, he says. The
fewer places [it gets modified], the better.
The researchers focused on incorrect and malicious answers provided by
DNS machines, Dagon says. The... alteration of DNS answers deserves
further study. In service of that goal, we will make data from the
ongoing study available to the research and DNS communities, he says.
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