FAQ: The DNS bug and you

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 Friday, when Dan Kaminsky, the security researcher who uncovered a critical flaw in the Doman 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 multi-vendor patch effort he helped coordinate.

However, the threat escalated last week after other researchers guessed some of the bug's technical details, and then increased even more 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, yourbestbanksite.com, 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 percent of DNS servers had not been patched. That number, however, is down from the 85 percent vulnerable in the first days after those patches were released.

Austrian security researchers issued a paper Thursday (download PDF) that claimed 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.

Kaminsky's blog has one. Click "Check My DNS" at the upper right under the "DNS Checker" heading.

DNS-OARC has a Web-based testing tool as well instructions on using the Unix "dig" command.

DNSstuff.com also boasts a Web testing tool. Click "Test Now" in the box at the lower left of the home page; the box is tagged as "DNS Vulnerability Check."

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What do I do if I'm vulnerable?

Patches are out, but as Kaminsky has said, this is really a problem for ISP (Internet Service Providers) and companies -- which maintain DNS servers -- to fix, rather than an end-user issue.

But that doesn't mean there's nothing for you to do.

If the testing tools show that you're vulnerable, you should contact your ISP or network administrator to ask what they're doing to plug the hole.

You should also apply any client-side patches that have been released. Microsoft, for instance, rolled out fixes on July 8 for Windows 2000, XP, Server 2003 and Server 2008. If you haven't applied the update spelled out in MS08-037, do so now.

According to a security advisory that Microsoft issued late last week -- after attack code geared to the DNS bug went public -- users who have installed the update are safe from attacks using the currently available exploits.

I use a Mac. What do I do?

Apple has not yet patched Mac OS X, a fact that hasn't escaped security researchers like Andrew Storms of nCircle and security consultants such as Rich Mogull.

As Mogull said in the story he wrote for TidBits last week: "Apple has not yet provided a patch, unlike dozens of other companies that make or distribute operating systems or DNS server software. Their customers are now in danger and Apple needs to respond immediately."

Fortunately, notes Mogull, attacks are much more likely against Mac servers than individual Macs, so though the later are technically vulnerable, "there's no need to panic."

My ISP isn't doing squat. What's my next move?

You can shift to other DSN servers, in effect abandoning those run by your ISP.

Several prominent security experts, including Kaminsky, have recommended OpenDNS, a free service that includes detailed instructions on how to steer your browser to its servers for DNS lookups by modifying settings in your operating system or router.