DNS May Be Patched, but Danger Still Lurks

We dodged a bullet last month -- the discovery of a fundamental flaw in the Domain Name System, Dan Kaminsky told a standing-room only (and some sitting on the floor) crowd at the Black Hat Briefings Wednesday. However, we can't count on our good luck continuing, he said.

Kaminsky, director of penetration testing for IOActive Inc., last month announced the unique coordinated multi-vendor release of a patch for the vulnerability, and he led a promotional effort to encourage organizations to install patches.

"There has been a remarkable amount of uptake on this patch," he said. Hundreds of millions of servers have been protected, Kaminsky added. Seventy percent of the Fortune 500 companies have tested and installed the patch on mail servers.

However, there are limits to the success. Another 15 percent have had problems installing the patch because of Network Address Translation, and 15 percent have not yet moved to install it.

"That's ridiculous," Kaminsky said. "We have to get better at fixing infrastructure. We got lucky this time. The next bug won't be as easy to deal with, and this one hasn't been easy."

Kaminsky discovered the bug about six months ago. Because it could affect virtually all name servers that translate domain names to IP addresses for Internet traffic, he did not go public with the news until major vendors had a chance to agree on a fix.

That fix was to increase the randomization of query IDs used to authenticate queries and responses. Adding port randomization raised the odds of guessing the right ID number from one in 65,000 to as little as one in 2 billion.

Kaminsky and the vendors have been criticized because the patch does not directly address the problem, and instead is a lowest-common denominator solution. Kaminsky defended the decision after illustrating ways to exploit the vulnerability.

"There are 15 ways of doing this attack," he said. "We chose a design that would make all of the attacks harder, not just the ones we know about."

One key of the patching strategy was to try to keep specific information about the vulnerability hidden for a month to give everyone a chance to install the patches. The goal met with only limited success.

"All patches can be reverse engineered," Kaminsky said, and the first details of the vulnerability were being worked out within two days of the July 8 announcement.

Owning DNS and being able to return false results to address queries could open a wide range of exploits on almost all kinds of Internet traffic, Kaminsky said. But the experience of the last month showed that cooperation among vendors works to improve safety.

"The industry did rally like we've never seen it rally before," he added.

About the Author

William Jackson is the senior writer for Government Computer News (


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