An ongoing cybersecurity threat has been identified, involving an unknown actor engaging in brute-force attacks on Linux SSH servers.
These attacks aim to compromise servers by installing a variety of malware, including the Tsunami DDoS bot, ShellBot, log cleaners, privilege escalation tools, and an XMRig coin miner. SSH (Secure Socket Shell), a widely used encrypted network communication protocol for remote server management, becomes a target when servers are inadequately secured, allowing threat actors to exploit vulnerabilities through repeated login attempts with different username-password combinations.
The campaign, recently discovered by AhnLab Security Emergency Response Center (ASEC), begins with the attackers scanning the internet for publicly-exposed Linux SSH servers. Upon identification, the threat actors proceed with brute-force attacks to gain unauthorized access. Once inside, they execute a command through a Bash script, fetching and running a collection of malware. ASEC observed that the attackers generate new SSH key pairs to maintain access, even if the user password is changed. The downloaded malware encompasses a range of malicious tools, including DDoS botnets, log cleaners, cryptocurrency miners, and privilege escalation tools. Among the malware deployed, ShellBot is a Perl-based DDoS bot utilizing the IRC protocol, supporting various attack methods such as port scanning, UDP, TCP, and HTTP floods, and capable of setting up a reverse shell.
Another DDoS botnet identified is Tsunami, with the specific version named “Ziggy,” a Kaiten variant. Tsunami, persisting between reboots, employs stealth techniques by writing itself on “/etc/rc.local” and uses typical system process names for concealment. The Tsunami botnet’s source code reveals its extensive capabilities, including various DDoS attack types and remote control commands for system manipulation and payload delivery. The attackers’ persistence and utilization of sophisticated malware highlight the importance of robust security measures to safeguard SSH servers against such threats.
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