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A sustained cyber-attack against a handful of niche pornography sites has demonstrated a novel way to inflict major damage on hardened targets using a modest amount of data, a security researcher has warned.

The technique - which tricks the net's authoritative name servers into bombarding innocent victims with more data than they can handle - is growing increasingly common, and it's likely only a matter of time before commercial attack kits add it to their arsenal, said Don Jackson, a researcher with Atlanta-based security provider SecureWorks. He also warned there is no easy fix because any remedy will potentially require settings for millions of DNS, or domain-name system, servers to be individually changed.

"The amplifiers in this attack are name servers configured to what is considered best practices," Jackson told The Register. Preventing the attack will require administrators to make changes to the software running each vulnerable DNS server on the internet, he added.

The attacks began in mid January and have used some 750,000 DNS servers to spew about 5Gbps worth of junk response packets at one victim alone, said Phil Rosenthal, CTO of ISPrime, an internet provider for one of the sites being attacked. Not bad work for a botnet that Jackson estimates is made up of fewer than 2,000 infected machines. The company has since been able to mitigate the attack using a variety of methods.

Representatives from NationalNet, which provides internet service to ladyboydolls.com, declined to comment. Attempts to reach representatives from the targeted porn sites were not successful.

The amplification technique exploits an artifact in the net's DNS from the days when it was considered harmless for a name server to respond to misdirected name queries with the name of a more appropriate server to make the request. Read together, RFCs 1034, 1035 and 1912 call for name servers that are queried for the location of the root servers to honor the request, Jackson and others say.

"There's really no reason to tell the requester that information," said Randal Vaughn, a professor of information systems at Baylor University and an expert in DNS amplification. "The problem is more related to the fact that at one time DNS servers would need to ask each other for help. When name servers started out, there were assumptions made that requests are legitimate, so we'll answer them."

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