DNS faces old and new cyberthreats

Despite attacks, Domain Name System security remains weak

When it comes to security, the Domain Name System has suffered from benign neglect. But old and emerging threats to the system that allows computer users to find Web sites will force technology managers to strengthen their DNS infrastructures, experts say.

DNS is the worldwide system for regulating Internet host names. It was designed to be efficient and easy for trusted users, but it lacks inherent security mechanisms, experts say. Moreover, many organizations run DNS services on general-purpose servers that are susceptible to vulnerabilities that hackers can exploit.

Some attacks can be subtle and hard to notice, said Marty Lindner, a senior member of the technical staff at the CERT Coordination Center. For example, domain cache poisoning allows hackers to redirect Web users to computers that they specify rather than the intended destinations.

Symantec's latest Internet Security Threat Report, issued in March, identifies Domain cache poisoning as one of the top attacks on government networks. The company bases its biannual update on cyberthreats on data gleaned from a broad sample of its worldwide private- and public- sector customers. Domain cache poisoning is not as prevalent in the private sector, Symantec officials say.

DNS is a hierarchy composed of domains — 265 so far, including .com, .org and country codes. DNS root and name servers act as address books, associating names of Web sites with IP addresses, said Jason Brvenik, a security engineering manager at Sourcefire, which sells equipment that detects and prevents intrusions.

Some organizations are not paying a lot of attention to DNS attacks because the system is "not being exploited in such a way that people are losing sleep over it," Lindner said. That's partly because attackers are doing so much damage in other ways that many companies don't think it's worth protecting DNS, he said.

Another factor is that the "damage by DNS attacks is not sufficiently big for [some] people to worry enough about it," said Johannes Ullrich, chief research officer at the SANS Institute.

Attacks are moving from Web servers that millions of people rely on to specific applications on a few servers that affect one or two companies, Ullrich said.

Playing the odds, most systems administrators don't protect against DNS attacks, and even companies that have been hit don't do much more than install software patches, Ullrich said. "Everyone is hoping it's not them," he said.

But that attitude could change as attacks increase. Symantec officials, who detected a rise in attacks on DNS infrastructures, advise organizations to properly maintain DNS servers and keep security software patches up-to-date.

There have been no new attacks on DNS in the past two to 12 months, depending on whom you ask. Unfortunately, "the problem with DNS is that the old attacks still work quite well," Ullrich said.

With domain cache poisoning, for instance, attackers can infiltrate the host file of an Internet service provider's or company's root server and insert bogus data to send traffic to their site instead.

When users look for the site, they end up at the impostors' address, Lindner said. As long as the root server's cache is not refreshed, tricked users always go back to the fake page, and attackers can make it so the cache doesn't refresh for years, he said.

Attackers can also direct only customers to their site to keep the site's administrators unaware, Lindner said. Users have little or no way to know that anything is wrong, he added.

Another popular DNS attack is domain name hijacking, in which hackers take control of a domain name by impersonating a legitimate administrative contact. They convince the registrars holding and transferring domain name licenses to sell them a site license by providing fake but plausible information, Ullrich said.

Registrars have made it more difficult to transfer ownership of site licenses, Ullrich said. It is possible now to lock a domain name and forbid its transfer, even if a requesting company has sufficient proof.

Even as the old threats continue, new ones are emerging, Lindner said.

Hacker Dan Kaminsky has developed a way to use the DNS architecture to create a covert channel for transferring files, Brvenik said. Currently effective only with small files, the technique doesn't use any protocols and can bypass nearly every firewall, he said.

A possible attack that DNS experts have not yet seen on a broad scale is pharming, a combination of phishing and domain cache poisoning, Ullrich said. A pharming attack would direct users to an exact copy of a Web site to collect their personal data, he said.

However, DNS will continue to be upgraded with more security, either piecemeal or all at once, Brvenik said.

Limited protection

The Internet Engineering Task Force has developed a secure version of the Domain Name System called DNS Security Extensions (DNSSEC), but it has limitations.

DNSSEC uses public-key infrastructure encryption to authenticate sites that its servers check, said Johannes Ullrich, chief research officer at the SANS Institute.

The problem is that DNSSEC is difficult to implement, slows users' systems and lacks a set of universally accepted keys, Ullrich said. Those who do buy the system turn off the keys, he added.

"DNSSEC has not reached a critical mass yet," he said. "It doesn't do you much good if everyone else isn't using it."

DNS users have other valid security options, said Jason Brvenik, a security engineering manager at Sourcefire. Two are widespread: HTTPS, the secure version of HTTP, and Secure Sockets Layer, denoted by the familiar yellow padlock in the bottom right corner of Web browser screens.

HTTPS and SSL still carry risks, but the protocols enable users to verify that they are actually at the Web site that appears on their screens, Brvenik said.

— Michael Arnone


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