Incident Response, Malware, TDR

Linux botnet observed launching powerful DDoS attacks

Threat actors are leveraging a botnet made up of infected Linux machines to launch powerful distributed denial-of-service (DDoS) attacks against as many as 20 targets per day, according to Akamai's Security Intelligence Response Team (SIRT).

The botnet is composed of Linux machines infected with a stealthy trojan identified in 2014 as "XOR DDoS." The threat was observed altering its installation depending on the victim's Linux environment and running a rootkit to avoid detection.

According to an advisory published on Tuesday, Akamai's SIRT has seen DDoS attacks – SYN and DNS floods were the observed attack vectors – that reached anywhere from a few gigabits per second (Gbps) to nearly 179 Gbps.

Although the advisory said that 90 percent of targets are located in Asia, Tsvetelin Choranov, security intelligence response engineer with Akamai's SIRT, told in a Tuesday email correspondence that a very small number of attacks have been launched against entities in the U.S.

“The target industries confirmed from our standpoint are online gaming and education,” Choranov said, adding, “We don't have a defined number of systems infected by this malware. Some of the source IPs that we are seeing actively producing malicious traffic have spoofing capabilities.”

The advisory noted that evidence suggests the malware is of Asian origin, but Choranov said that Akamai's SIRT has not heard of anyone claiming responsibility for the DDoS attacks. He added that there is also no known reason for the attacks, such as extortion.

Unlike a lot of malware, XOR DDoS is not spreading via exploitation of vulnerabilities.

“Rather, it populates via Secure Shell (SSH) services that are susceptible to brute-force attacks due to weak passwords,” the advisory said. “Once login credentials have been acquired, the attackers [use] root privileges to run a Bash shell script that downloads and executes the malicious binary.”

The advisory outlines two methods for detecting the malware.

“To detect this botnet in your network, you can look for the communications between a bot and its C2, using the Snort rule shown in [the advisory],” the advisory said. “To detect infection of this malware on your hosts you can use the YARA rule [also in the advisory].”

XOR DDoS is persistent, meaning it runs processes that will reinstall deleted files. Removing the threat involves identifying malicious files in two directories, identifying the processes responsible for persistence of the main process, killing those processes, and deleting the malicious files.

“XOR DDoS malware is part of a wider trend of which companies must be aware: Attackers are targeting poorly configured and unmaintained Linux systems for use in botnets and DDoS campaigns,” the advisory said.

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