Security news that informs and inspires

Hacker History: How Dan Kaminsky Almost Broke the Internet


In the summer of 2008, security researcher Dan Kaminsky disclosed how he had found a huge flaw in the Internet that could let attackers redirect web traffic to alternate servers and disrupt normal operations. In this Hacker History video, Kaminsky describes the flaw and notes the issue remains unfixed.

“We were really concerned about web pages and emails 'cause that’s what you get to compromise when you compromise DNS,” Kaminsky says. “You think you’re sending an email to IBM but it really goes to the bad guy.”

As the phone book of the Internet, DNS translates easy-to-remember domain names into IP addresses so that users don’t have to remember strings of numbers to reach web applications and services. Authoritative nameservers publish the IP addresses of domain names. Recursive nameservers talk to authoritative servers to find addresses for those domain names and saves the information into its cache to speed up the response time the next time it is asked about that site. While anyone can set up a nameserver and configure an authoritative zone for any site, if recursive nameservers don’t point to it to ask questions, no one will get those wrong answers.

We made the Internet less flammable.

Kaminsky found a fundamental design flaw in DNS that made it possible to inject incorrect information into the nameserver's cache, or DNS cache poisoning. In this case, if an attacker crafted DNS queries looking for sibling names to existing domains, such as,, and, while claiming to be the official "www" server for, the nameserver will save that server IP address for “www” in its cache.

“The server will go, ‘You are the official. Go right ahead. Tell me what it’s supposed to be,’” Kaminsky says in the video.

Since the issue affected nearly every DNS server on the planet, it required a coordinated response to address it. Kaminsky informed Paul Vixie, creator of several DNS protocol extensions and application, and Vixie called an emergency summit of major IT vendors at Microsoft’s headquarters to figure out what to do.

The “fix” involved combining the 16-bit transaction identifier that DNS lookups used with UDP source ports to create 32-bit transaction identifiers. Instead of fixing the flaw so that it can’t be exploited, the resolution focused on making it take more than ten seconds, eliminating the instantaneous attack.

“[It’s] not like we repaired DNS,” Kaminsky says. “We made the Internet less flammable.”

DNSSEC (Domain Name System Security Extensions), is intended to secure DNS by adding a cryptographic layer to DNS information. The root zone of the internet was signed for DNSSEC in July 2010 and the .com Top Level Domain (TLD) was finally signed for DNSSEC in April 2011. Unfortunately, adoption has been slow, even ten years after Kaminsky first raised the alarm about DNS, as less than 15 percent of users pass their queries to DNSSEC validating resolvers.

The Internet was never designed to be secure. The Internet was designed to move pictures of cats.

No one expected the Internet to be used for commerce and critical communications. If people lose faith in DNS, then all the things that depend on it are at risk.

“What are we going to do? Here is the answer. Some of us gotta go out fix it,” Kaminsky says.