Leet Botnet vies with Mirai for 2016 DDoS crown
Leet Botnet vies with Mirai for 2016 DDoS crown

The Leet Botnet may have wrested the 2016 crown as most powerful distributed denial of service (DDoS) attack from Mirai with a 650 Gigabit per second (Gbps) attack launched early last week.

Avishay Zawonzi and Dima Bekerman, researchers at Imperva Security, wrote that a DDoS incident that took place on December 21 rivaled what was thought to be the largest such attack this year when KrebsonSecurity was struck in September with an attack that ranged between 620 and 665 Gbps.

However, the two attacks, along with the massive Mirai botnet attack this fall, are much different than Leet. The attacks were picked up on the Imperva Incapsula network as the malicious actors apparently tried to strike several Imperva customers. When that failed, they turned to hitting Imperva itself, the researchers said.

The first burst of activity hit at 10:55 a.m. on December 21.

“The first DDoS burst lasted roughly 20 minutes, peaking at 400 Gbps,” Zawonzi and Bekerman wrote. "Failing to make a dent, the offender regrouped and came back for a second round. This time enough botnet “muscle” to generate a 650 Gbps DDoS flood of more than 150 million packets per second (Mpps)."

The attack did not impact Imperva's site and, the researchers said, the initial failure to penetrate through to the company's customers indicates a failure by the attackers.

“It's hard to say why this attack didn't focus on a specific customer,” the researchers stated. "Most likely, it was the result of the offender not being able to resolve the IP address of his actual victim, which was masked by Incapsula proxies."

The bad actors used spoofed IPs to keep their location hidden and to obfuscate what kind of devices were used to launch the attack, but it was determined that the botnet used thousands of compromised devices. Mirai's owners used DVRs and other IoT devices.

An analysis of the payload showed the attack was generated by two different SYN payloads – SYN packets ranging in size from 44 to 60 bytes and abnormally large packets of 799 to 936 bytes.

“The former was used to achieve high Mpps packet rates, while the latter was employed to scale up the attack's capacity to 650 Gbps,” Imperva said.

The fact that SYN packets were used indicates that Leet and Mirai are entirely different creatures. The blog noted that Mirai is not designed to carry out large SYN attacks, Mirai has hardcoded TCP options (MSS, SACK, TSVAL, WSS), which weren't present in 99.99% of the payloads and, finally, Mirai payloads are generated from random strings.

The only sign of who was behind this attack was the signature “1337,” left in the TCP header.