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One in ten DNS servers still vulnerable to poisoning

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Four months after researchers warned of a nasty design flaw in the net's address lookup system, more than 10 per cent of the servers used to resolve domain names on the internet remain "trivially vulnerable" to attack, a new study concludes.

That translates to about 1.3 million domain name system servers that still have not patched against the cache poisoning flaw discovered earlier this year, according to the report, commissioned by DNS hardware supplier Infoblox. Since early July, researcher Dan Kaminsky and a choir of other security experts have been imploring internet service providers, corporations, and large organizations to protect themselves against the flaw by patching programs such as BIND, which helps translate domain names into IP addresses.

"Assuming there are people out there using those name servers, they are in a very, very dangerous situation," said Cricket Liu, vice president of architecture at Infoblox and an author of several books concerning DNS. "This is a really, really serious attack."

The report found that an even larger percentage of the net's name servers - an estimated 44 percent - could be used by miscreants to launch devastating attacks on unwitting third parties. That's because the name servers are available to anyone on the internet rather than only to the members of the company or organization that operates them. In such attacks, perpetrators send so-called recursive DNS servers fraudulent queries that appear to come a victim's computer. The recursive DNS servers then overwhelm the target with more data than it can handle.

The results are part of Infoblox's fourth annual survey of DNS servers. It randomly selected 99.3 million IP addresses and name servers authoritative for 1 million .com and .net domain names. Researchers sent a simple DNS query to each probe address and - based on the result - estimated there are some 11.9 million name servers running on the internet.

The researchers estimated that there are 4.3 million open resolvers on the net that reply to a query. The vast majority of them, at 89 percent, were running version 9 of BIND. BIND 8, bboy MyDNS, and DJ Bernstein TinyDNS ranked second, third, and fourth respectively.

Of the 44 per cent of name servers found to be recursive, 25 per cent of those failed to properly randomize the source ports that send lookup information. As a result, they are vulnerable to Kaminsky's cache poisoning vulnerability. What's more, 30 per cent of DNS servers surveyed permitted zone transfers to arbitrary requesters, which also leaves machines open to denial-of-service attacks.

The patch Kaminsky and others fashioned after discovery of the cache poisoning flaw randomizes the ports DNS servers use to thwart attackers who flood machines with fraudulent results. Results that don't include the correct transaction ID and randomized port number are rejected. The fix is viewed as a temporary measure whose effectiveness will dilute over time.

Over the long term, security experts are looking to a technology known as DNSSec to solve the problem. That involves cryptographically signing the internet's DNS records to guard against forgeries. DNSSec was first proposed in 1999. It has undergone something of a renaissance since Kaminsky took his discovery public.

But so far, Infoblox has found little evidence of widespread use. Just 0.002 percent of DNS zones it tested supported the extensions.

"I had hoped we would see a spike in the adoption of DNSSec, but we really didn't see much of anything," Liu told El Reg. "It says that awareness of DNSSec is not that high, and the people who do know about DNSSec are probably afraid of it." ®

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