Windows Executable Masks Mac Malware

A new strain of MacOS malware disguises itself as a Windows executable file to evade detection and embed itself on a system. But the malware authors aren't exactly in the cross-platform avant-garde: the .EXE file that carries the MacOS malware will not, in fact, execute on a Windows machine.

Welcome to the malware rabbit hole.

Researchers from Trend Micro discovered the malware inside the installer for a popular firewall and network monitor called Little Snitch. Inside the standard MacOS .DMG installer is a .EXE file that is part of the mono framework — technology that's used to allow .NET applications to run across multiple platforms, including MacOS.

The application that begins execution scans the host system for a variety of machine and environment information and sends the data to a C&C server. It then downloads potentially unwanted applications (PUAs) that include adware camouflaged as Adobe Flash and a copy of Little Snitch that might, in itself, be compromised.

Malware authors typically use higher-level executables, like Adobe Flash files, JavaScript, or PHP to move between platforms. Most of those file types are now scanned by malware protection software and blocked if malicious behavior is detected.

Because .EXE files will not on their own execute on MacOS, MacOS anti-malware packages don't typically scan or block them. This attack is aimed squarely at Macs: The .EXE file used to deliver the malware payload returns an error message if someone tries to run it on a Windows system.

According to the researchers, this particular implementation of the new technique is likely a research project on the part of malware authors. "We think that the cybercriminals are still studying the development and opportunities from this malware bundled in apps and available in torrent sites, and therefore we will continue investigating how cybercriminals can use this information and routine," they wrote in their post on the findings.

As for how to avoid this attack, some anti-malware packages are beginning to pick up and scan these .EXE files for malicious intent. If your organization doesn't have such software, then be sure that multi-layer security is in place and remind users to only download applications from fully vetted and verified sources.

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