How is cross-platform malware carried in Word docs?

Researchers at Fortinet Inc. recently discovered a sample of cross-platform malware, a type of malware designed to infect either Windows systems or macOS systems depending on which operating system the victim is using. The malware is being spread through Microsoft Word documents. How does cross-platform malware execute on different operating systems?

Cross-platform development environments have long been a goal for many application developers because the environments free them to focus on functionality and widespread adoption, instead of having to know the intricacies of different platforms to make their application work. This means the application development environment has to be able to compile the code to binaries for all the targeted operating systems or for an application execution environment, like the Java Runtime Environment, for the code to execute.

Malware authors share that goal, as it enables them to infect the most systems. Researchers at Fortinet analyzed a new piece of cross-platform malware targeting Windows and macOS systems.

Instead of using Java for the code execution, this cross-platform malware uses a Microsoft Word document with a macro to call built-in scripting languages to run the malicious code on the endpoint. The malicious macro detects the target system's operating system, and then uses Python on macOS systems or PowerShell on Windows systems to execute the malicious code. The script then calls out to an external system to download the rest of the cross-platform malware.

Protection from malicious Word docs should be a standard part of an enterprise's information security controls. Fortinet released indicators of compromise for the cross-platform malware, and it has added network detections now.

Adding the malicious URLs to network controls to block endpoints from downloading the additional malware can prevent the infected systems from being completely taken over.