It’s safe to say that the last few years have been eventful when it comes to the Internet of Things (IoT) threat landscape, with new waves of distributed denial of service (DDoS) bots emerging with increasing regularity. Ever since the first reported incident of the Mirai botnet (Linux.Mirai) back in 2016, followed by the malware’s source code being leaked, the number of variants of this family has been growing steadily, their success helped along by an environment of poorly managed IoT devices. As it is, the IoT market is hugely fragmented and most of the devices do not receive software patches for the known vulnerabilities. To make things worse, the malware authors continue to evolve these variants, making the malware more powerful and portable across different platforms and architectures.

Leveraging open-source projects

One of the major pain points for a cross-platform IoT botnet is portability. The malware must be able to run on different architectures and platforms in a self-contained capsule without any runtime surprises or misconfiguration. This is also an area where many inexperienced malware authors, or script-kiddies, fail if they simply copy/paste and reuse the existing malware code base.

At the end of July, I came across a live remote server hosting multiple malware variants, each for a specific platform. As with many Mirai infections, it starts by firing a shell script on a vulnerable device. That shell script sequentially tries downloading and executing individual executables one by one until a binary compliant with the current architecture is found.