Linux-Targeted Malware Increases by 35% in 2021: XorDDoS, Mirai and Mozi Most Prevalent

Linux powers most of today’s cloud infrastructure and web servers, yet it also powers mobile and IoT devices. It’s popular because it offers scalability, security features and a wide range of distributions to support multiple hardware designs and great performance on any hardware requirements.

With various Linux builds and distributions at the heart of cloud infrastructures, mobile and IoT, it presents a massive opportunity for threat actors.
For example, whether using hardcoded credentials, open ports or unpatched vulnerabilities, Linux-running IoT devices are a low-hanging fruit for threat actors – and their en masse compromise can threaten the integrity of critical internet services.
More than 30 billion IoT devices are projected to be connected to the internet by the end of 2025, creating a potentially very large attack surface for threats and cybercriminals to create massive botnets.

A botnet is a network of compromised devices connected to a remote command-and-control (C2) center. It functions as a small cog in the larger network, and can infect other devices. Botnets are often used for DDoS attacks, spamming targets, gaining remote control and performing CPU-intensive activities like cryptomining.
DDoS attacks use multiple internet-connected devices to access a specific service or gateway, preventing legitimate traffic from passing through by consuming the entire bandwidth, causing it to crash.

XorDDoS is a Linux trojan compiled for multiple Linux architectures, ranging from ARM to x86 and x64.
Its name is derived from using XOR encryption in malware and network communication to the C2 infrastructure.

When targeting IoT devices, the trojan is known to use SSH brute-forcing attacks to gain remote control on vulnerable devices.

On Linux machines, some variants of XorDDoS show that its operators scan and search for Docker servers with the 2375 port open.
This port offers an unencrypted Docker socket and remote root passwordless access to the host, which attackers can abuse to get root access to the machine.

Mozi is a peer-to-peer (P2P) botnet network that utilizes the distributed hash table (DHT) system, implementing its own extended DHT.
The distributed and decentralized lookup mechanism provided by DHT enables Mozi to hide C2 communication behind a large amount of legitimate DHT traffic.
The use of DHT is interesting because it allows Mozi to quickly grow a P2P network.
And, because it uses an extension over DHT, it’s not correlated with normal traffic, so detecting the C2 communication becomes difficult.

Mozi infects systems by brute-forcing SSH and Telnet ports.
It then blocks those ports so that it is not overwritten by other malicious actors or malware.

Mirai malware has made a name for itself in the last few years, especially after its developer published Mirai’s source code.
Similar to Mozi, Mirai abuses weak protocols and weak passwords, such as Telnet, to compromise devices using brute-forcing attacks.

With multiple Mirai variants emerging since its source code became public, the Linux trojan can be considered the common ancestor to many of today’s Linux DDoS malware.
While most variants add onto existing Mirai features or implement different communication protocols, at their core they share the same Mirai DNA.