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FAQ: The DNS bug and you

Attack code hit the street last week, so what's your move?

July 28, 2008 12:00 PM ET

Computerworld - You know a bug is big news when it makes National Public Radio's All Things Considered, the network's afternoon drive-time show.

That's what happened on Friday, when Dan Kaminsky, the security researcher who uncovered a critical flaw in the Domain Name System (DNS) software used to direct traffic on the Internet, gave a synopsis of the problem and what has been done to fix it.

Computerworld readers, of course, have known about the threat since July 8, when Kaminsky announced the vulnerability and talked about the multivendor patch effort he helped coordinate.

However, the threat escalated last week after other researchers guessed some of the bug's technical details, and it then increased even more a few days later, when attack code went public.

Are you at risk? If so, what do you do about it? We'll tackle those questions and a few others.

What's all the fuss? A basic flaw in the Domain Name System makes it much easier than originally thought to insert bogus information into the Internet's routing infrastructure.

Successful "cache poisoning" attacks let hackers reroute users' requests to, say,, to one that looks like Your Best Bank but is in fact a fake created to dupe people into entering confidential information, such as their online banking usernames and passwords. All of this happens silently and behind the scenes, so no one's the wiser.

Here's how Kaminsky put it: "A bad guy has a 1-in-65,000 chance of stealing your Internet connection, and he can try a couple thousand times a second."

By the way, this explanation by Kaminsky is among the few around we think is understandable to the DNS layman. Recommended reading.

Patches are out, right? So what's the problem? Yes, some vendors issued patches on July 8 as part of a coordinated release. But not all DNS servers have been fixed.

Far from it, in fact, according to the available numbers.

Kaminsky, who tracks the results users get when they run the testing tool on at his blog (see "How do I know if I'm vulnerable," next section) said Saturday that at least 52% of DNS servers had not been patched. That number, however, is down from the 85% vulnerable in the first days after those patches were released.

Austrian security researchers issued a paper on Thursday (download PDF) claiming that more than two-thirds of that country's DNS servers remained unpatched, a situation they called "rather grim."

How do I know if I'm vulnerable? Several free online tools will tell you whether the DNS resolving server you use has been patched.

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