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By | Dan Goodin 11th December 2007 22:57

Rogue servers point users to impostor sites


Researchers have uncovered a large network of rogue servers that threatens end users by silently feeding them counterfeit versions of trusted websites.

It's the internet equivalent of a telephone directory service intentionally giving an incorrect listing when someone asks for the number for Bank of America. Instead of directing a victim to the intended website, about 68,000 servers point to impostor sites, according to the team of researchers from Google and the Georgia Institute of Technology.

They found hundreds of addresses every week that triggered malware that silently changed configuration settings so operating systems, unbeknown to the users, would use the rogue DNS lookups instead of trusted ones. Once that change was made, criminals controlling the servers had the ability to forge the pages when infected users tried to visit virtually any website. The malware effecting such drive-by alterations typically involved a single line of code, making the attack very easy to carry out, said David Dagon, a Georgia Tech researcher who co-authored the paper.

"Instead of having to write an elegant rootkit or a clever buffer overflow or wait for a vulnerability to be found and pounce, the malware writers are saying: 'We'll rewrite people's DNS settings,'" Dagon said. "It's a crime with few witnesses."

The researchers found about 17 million open recursive DNS servers serving the IPv4 address space. Of those, 2.4 per cent were found to give incorrect information. The vast majority - two per cent - were merely providing what is known as "DNS error path correction," which attempts to correct minor typos and isn't intended to deceived users. The remaining 0.4 per cent provided outright false information that was intended to mislead.

Spoofed websites included Bank of America and

Many of the "DNS liars" impersonated sites in an attempt to harvest user credentials and perform man-in-the-middle attacks. Others simply tried to drive traffic to their sites by redirecting users to parked pages loaded with ads and porn. In some cases, the impostors acted as proxies to the sites being spoofed, but ads or other content would be superimposed on top.

"From the user's perspective, it look like the internet was working just fine - except that a different group of people made money off the ads, and search results could be altered," Dagon said.

The study, titled "Corrupted DNS Resolution Paths: The Rise of a Malicious Resolution Authority," is scheduled to be published in February by the Network and Distributed System Security Symposium in San Diego. Other co-authors include Chris Lee and Wenke Lee, of Georgia Tech, and Niels Provos of Google. ®

This story was updated to correct the number of servers pointing to impostor sites</i.>.

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