Another Massive DDoS Closes Out 2016, But Mirai Not To Blame

This past year has been one for the record books when it comes to distributed denial of service (DDoS) attacks, so it is only proper that 2016 closes out with news of another massive DDoS attack, reported by Imperva researchers. According to them, the Imperva Incapsula network was forced to mitigate a 650 Gbps DDoS attack just a few days before Christmas.

One of the largest DDoS attacks on record, this particular assault is notable because it strayed from the bad guys' recent DDoS playbook. For much of the year, attackers have been testing the bounds of DDoS traffic-pushing capabilities using the advanced Mirai botnet, which consists of hijacked IoT devices. This time around, Imperva researchers say the holiday attack came at the hands of a new malicious network it calls Leet Botnet.

Earlier this fall, Mirai was behind the 620 Gbps attack against KrebsOnSecurity.com, a 990 Gbps attack against French hosting provider OVH that reportedly utilized a network that could have been capable of pushing up to 1.5 Tbps in malicious traffic, and the massive DDoS in October against DNS provider Dyn that reached an estimated 1.2 Tbps in malicious traffic. To pull off these attacks, Mirai primarily relied on tens of thousands of IoT devices, most of which were compromised CCTV cameras and DVR machines.

Imperva researchers report that spoofed IPs make it impossible to figure out what kind of devices carried out the Christmas attack. Their analysis of the payload does at least lead them to conclusively determine it was another botnet wreaking havoc.

"So far, all of the huge DDoS attacks of 2016 were associated with the Mirai malware," wrote Avishay Zawoznik and Dima Bekerman of Imperva. "However, the payload characteristics clearly show that neither Mirai nor one of its more recent variants was used for this assault."

Like many recent DDoS attacks, the Leet Botnet used a combination of both large and small SYN packet sizes "to both clog network pipes and bring down network switches," the pair wrote. The smaller packets were used to push up packet rates up past 150 million packets per second (Mpps), while the larger ones were used to increase the overall attack capacity. Imperva dubbed the botnet Leet because of a 'signature' left in some of the TCP Options headers of the smaller packets that spelled out "1337."

What really interested researchers, though, was Leet's larger payloads, which were populated by shredded lists of IP addresses that indicated Leet was accessing local files of compromised devices and scrambling them up to generate its payloads.

"Basically, the entire attack was just a mishmash of pulverized system files from thousands upon thousands of compromised devices," Zawoznik and Bekerman wrote. "It makes for an effective obfuscation technique that can be used to produce an unlimited number of extremely randomized payloads. Using these payloads, an offender can circumvent signature-based security systems that mitigate attacks by identifying similarities in the content of network packets." 

This year we saw DDoS attacks escalate to record heights and these high-powered botnets are a symptom of the times.

So far, all of the huge DDoS attacks of 2016 were associated with the Mirai malware. However, the payload characteristics clearly show that neither Mirai nor one of its more recent variants was used for this assault.

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