New Tsunami botnet targets Linux SSH servers

Researchers warn of an ongoing Tsunami DDoS botnet campaign targeting inadequately protected Linux SSH servers.

Researchers from AhnLab Security Emergency response Center (ASEC) have uncovered an ongoing hacking campaign, aimed at poorly protected Linux SSH servers, to install the Tsunami DDoS botnet (aka Kaiten). The threat actors behind these attacks were also observed installing other malware families, including ShellBot, XMRig CoinMiner, and Log Cleaner.

The Tsunami DDoS botnet operates as an IRC bot and relies on IRC for C2 communication.

The researchers pointed out that the source code of the Tsunami bot is publicly available allowing multiple threat actors to create their own botnet. The bot primarily targets IoT devices along with Linux servers with brute force attacks.

The following table contains the list ID and password values used by the bot in the dictionary attacks along with the IP address for the target.

Upon successfully logging in, the attackers execute a command to download and run various malware.

The downloader-type Bash script is used to install additional malware and perform various preliminary tasks to take control of infected systems, including the creation of a backdoor SSH account.

Threat actors also generated a new pair of public/private SSH keys for the compromised server to achieve persistent access, even if the user password was changed.

The variant of the Tsunami bot employed in this campaign is a Kaiten variant known as Ziggy, it maintains persistence by writing itself on the “/etc/rc.local” file.

In order to avoid detection, the bot attempts to change the name of the process that is currently running to “[kworker/0:0]”. Using this threat the malware uses normal process names, making it difficult for users to notice.

The Tsunami botnet supports multiple DDoS attack techniques, including SYN, ACK, UDP, and various flood DDoS methods.

Tsunami also supports multiple commands, including collecting system information, executind shell commands, establishing reverse shells, collecting system information, updating itself, downloading additional payloads, and killing itself.

The attackers also use a privilege escalation malware, it is an ELF malware that set the user ID and group ID as the root account before executing the shell.

“Attack campaigns on poorly managed Linux SSH servers have been occurring persistently for quite some time. The threat actor installed XMRig CoinMiner alongside DDoS bots like Tsunami and ShellBot on infected systems.” concludes the report. “administrators should use passwords that are difficult to guess for their accounts and change them periodically to protect the Linux server from brute force attacks and dictionary attacks and update to the latest patch to prevent vulnerability attacks. They should also use security programs such as firewalls for servers accessible from outside to restrict access by attackers. Finally, caution must be practiced by updating V3 to the latest version to block malware infection in advance.”

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Pierluigi Paganini

(SecurityAffairs – hacking, Tsunami botnet)