Home Scripts Mac malware uses ‘run-only’ AppleScripts to evade analysis

Mac malware uses ‘run-only’ AppleScripts to evade analysis

7 min read

A cryptocurrency mining marketing campaign focusing on macOS is utilizing malware that has advanced into a fancy variant giving researchers quite a lot of bother analyzing it.

The malware is tracked as OSAMiner and has been within the wild since at the very least 2015. But, analyzing it’s tough as a result of payloads are exported as run-only AppleScript information, which makes decompiling them into supply code a tall order.

A not too long ago noticed variant makes analyzing much more tough because it embeds a run-only AppleScript into one other scripts and makes use of URLs in public internet pages to obtain the precise Monero miner.

Reversing run-only AppleScript

OSAMiner sometimes spreads by way of pirated copies of video games and software program, League of Legends and Microsoft Workplace for macOS being among the many extra in style examples.

The malware has been researched prior to now [1, 2] however the run-only AppleScript file hindered full evaluation, limiting it to observing the conduct of the pattern.

AppleScript information embrace each the supply and the compiled code however enabling “run-only” saves solely the compiled model so the human-readable code is not obtainable, thus eradicating the potential of reverse engineering.

Safety researchers at Sentinel One found on the finish of 2020 a brand new pattern of OSAMiner that difficult “the already tough course of of study.”

Nonetheless, they have been capable of reverse engineer some samples they collected through the use of a less-known AppleScript disassembler (Jinmo’s applescript-disassembler) and a decompiler device developed internally referred to as aevt_decompile.

Evasion actions

The current OSAMiner campaigns use three run-only AppleScript information to deploy the mining course of on the contaminated macOS machine, Sentinel One discovered:

  • a guardian script that executes from the trojanized software
  • an embedded script
  • the miner setup AppleScript

The primary position of the guardian script is to put in writing the embedded AppleScript to ~/Library/okay.plist utilizing a “do shell script” command and execute it. It additionally checks if the machine has sufficient free house and exits if there is not ample storage.

Different duties it runs embrace accumulating the serial variety of the gadget, restarting the ‘launchctl’ job answerable for loading and unloading daemons or brokers, and to kill the Terminal software.

The researchers say that the principle script additionally units up a persistence agent and downloads the primary stage of the miner from a URL set on a public web page.

Some samples might not result in a dwell URL. Nonetheless, Sentinel One was capable of finding an energetic one (https://www[.]emoneyspace[.]com/wodaywo) and seen that the malware parsed a hyperlink within the supply code of the web page that pointed to a PNG picture.

This was the third run-only AppleScript, downloaded to the ~/Library/11.PNG. Its goal is to obtain the open-source XMR-Stak Monero miner that works on Linux, Home windows, and macOS.

“The setup script consists of pool handle, password and different configuration info however no pockets handle,” the researchers say in a report at this time, including that it additionally makes use of the “caffeinate” device to stop the machine from coming into sleep mode.

Evading detection

In response to Sentinel One, the second script is meant to stop evaluation and evade detection. Supporting this conclusion is killing the Exercise Monitor, which is the equal of the Process Supervisor in Home windows, prone to stop customers from checking the system’s useful resource utilization.

Moreover, the script is designed to kill processes belonging to in style instruments for system monitoring and cleansing. It finds them by checking a hardcoded checklist.

Sentinel One says that whereas AppleScript incorporates extra highly effective options [1, 2], the authors of OSAMiner should not at the moment taking benefit. That is seemingly as a result of the present setup allowed them to run their cryptocurrency mining campaigns with little resistance from the safety group.

Nonetheless, as Sentinel One proved, the approach just isn’t infallible and researchers have the means to investigate it and put together defenses towards different malware that will select to make use of it.

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