DNS Inventor Warns of Next Big Threat

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 reported.

“This report demonstrates that people are getting lured out to dark alleyways of the Internet. The actual damage isn’t 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 Tech’s 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.”

Nominum’s 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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