• Security researchers from Group-IB discover unique new piece of malware
  • It abuses extended attributes for macOS files to deploy the payload
  • The malware is most likely built by North Korean state-sponsored actors

Cybersecurity researchers have stumbled upon yet another malware variant for macOS likely built by the notorious North Korean Lazarus group.

The report from Group-IB concerns the discovery of RustyAttr, a brand new piece of macOS malware built using the Tauri framework. T

he malware was not flagged on VirusTotal and was, at one point, signed using a legitimate Apple developer ID. The ID has since been revoked.

Extended attributes

Days before them, researchers from Jamf found something similar - a seemingly benign app on VirusTotal, built with Flutter, and serving as a backdoor for macOS victims.

In both cases, the malware used novel obfuscation methods, but wasn’t fully operational, leading the researchers to believe that they were mere experiments, as crooks look for new ways to hide the infection.

RustyAttr was found abusing extended attributes for macOS, the researchers claim.

Extended attributes (xattrs) are a feature that allows files and directories to store additional metadata beyond standard attributes like name, size, and permissions. They are used for different things, from storing security-related information, to tagging files with specific metadata, and enabling compatibility with other file systems. In this case, the EA name was “test”, and carries a shell script.

When the malware runs, it loads a website with a piece of JavaScript. This JavaScript - called preload.js, pulls content from “test” which seems to be a location. This location is then sent to the ‘run_command’ function, where the shell script executes it.

While the process is ongoing, the victim is tricked with a decoy PDF file or a fake error message that pops up in the foreground.

RustyAttr was most likely built by Lazarus, the researchers said, although since there are no reported victims, they cannot be absolutely certain. However, they are confident that the malware was built to test new delivery and obfuscation methods on macOS devices.

Via BleepingComputer

You might also like