Microsoft Warns of 'Stealthy DDoS Malware' Targeting Linux Devices

'In the last six months, we observed a 254% increase in activity from a Linux trojan called XorDdos,' writes the Microsoft 365 Defender Research Team. It's a trojan combining denial-of-service functionality with XOR-based encryption for communication.

Microsoft calls it part of 'the trend of malware increasingly targeting Linux-based operating systems, which are commonly deployed on cloud infrastructures and Internet of Things devices.' And ZDNet describes the trojan 'one of the most active Linux-based malware families of 2021, according to Crowdstrike.'

XorDdos conducts automated password-guessing attacks across thousands of Linux servers to find matching admin credentials used on Secure Shell (SSH) servers... Once credentials are gained, the botnet uses root privileges to install itself on a Linux device and uses XOR-based encryption to communicate with the attacker's command and control infrastructure.

While DDoS attacks are a serious threat to system availability and are growing in size each year, Microsoft is worried about other capabilities of these botnets. 'We found that devices first infected with XorDdos were later infected with additional malware such as the Tsunami backdoor, which further deploys the XMRig coin miner,' Microsoft notes... Microsoft didn't see XorDdos directly installing and distributing the Tsunami backdoor, but its researchers think XorDdos is used as a vector for follow-on malicious activities...

XorDdoS can perform multiple DDoS attack techniques, including SYN flood attacks, DNS attacks, and ACK flood attacks.

Microsoft's team warns that the trojan's evasion capabilities 'include obfuscating the malware's activities, evading rule-based detection mechanisms and hash-based malicious file lookup, as well as using anti-forensic techniques to break process tree-based analysis.

'We observed in recent campaigns that XorDdos hides malicious activities from analysis by overwriting sensitive files with a null byte. It also includes various persistence mechanisms to support different Linux distributions.'

Read more of this story at Slashdot.