Sat Oct 22, 2016, 10:01 AM

How the Dyn DDoS attack unfolded


The DDoS attack force included 50,000 to 100,000 internet of things (IoT) devices such as cameras and DVRs enslaved in the Mirai botnet, as well as an unknown number of other devices that are parts of other botnets, says Dale Drew, CTO of Level 3. He theorizes the mastermind behind the attack hired multiple botnets to compile the number wanted for the attacks.

It seems careful planning went into the attacks in order to insure that Dyn’s services were crippled worldwide, says Nick Kephart, Network Outage Analyst at ThousandEyes.

He says the first wave of the attack came against three Dyn data centers – Chicago, Washington, D.C., and New York - affecting mainly the East Coast of the U.S. because DNS lookups are routed to the nearest data center.

The second wave, which he says was ongoing at 7 p.m. Eastern time, hit 20 Dyn data centers around the world. This phase of the attack required extensive planning. Since DNS request go to the closest DNS server, that means the attacker had to plan a successful attack for each of the 20 data centers. That means having for enough bots in each region to be able to take down the local Dyn services, he says.

Drew says the attack consisted mainly of TCP SYN floods aimed directly at against port 53 of Dyn’s DNS servers, but also a prepend attack, which is also called a subdomain attack. That’s when attackers send DNS requests to a server for a domain for which they know the target is authoritative. But they tack onto the front of the domain name random prepends or subnet designations. The server won’t have these in its cache so will have to look them up, sapping computational resources and effectively preventing the server from handling legitimate traffic, he says.

This was only a limited attack. "He says that Mirai, the malware behind gigantic IoT botnets, was involved. About 10% to 20% of all the 500,000 or so known Mirai bots were involved, but so were other devices."

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