Cyble Research and Intelligence Lab recently unearthed an elaborate, multi-stage malware attack targeting not only job seekers but also digital marketing professionals. The hackers are a Vietnamese threat actor who was utilising different sophisticated attacks on systems by making use of a Quasar RAT tool that gives a hacker complete control of an infected computer. 

Phishing emails and LNK files as entry points

The attack initiates with phishing emails claiming an attached archive file. Inside the archive is a malicious LNK, disguised as a PDF. Once the LNK is launched, it executes PowerShell commands, which download additional malicious scripts from a third-party source, thus avoiding most detection solutions. The method proves very potent in non-virtualized environments in which malware remains undiscovered inside the system.

Quasar RAT Deployment

Then, the attackers decrypt the malware payload with hardcoded keys. Quasar RAT - a kind of RAT allowing hackers to obtain total access over the compromised system - is started up. Data can be stolen, other malware can be planted, and even the infected device can be used remotely by the attackers.

The campaign targets digital marketers primarily in the United States, using Meta (Facebook, Instagram) advertisements. The malware files utilised in the attack were designed for this type of user, which has amplified its chances.

Spread using Ducktail Malware

In July 2022, the same Vietnamese threat actors expanded their activities through the launch of Ducktail malware that specifically targeted digital marketing professionals. The group included information stealers and other RATs in its attacks. The group has used MaaS platforms to scale up and make their campaign versatile over time.

Evasion of Detection in Virtual Environments

Its superiority in evading virtual environment detection makes this malware attack all the more sophisticated. Here, attackers use the presence of the "output.bat" file to determine whether it's running in a virtual environment or not by scanning for several hard drive manufacturers and virtual machine signatures like "QEMU," "VirtualBox," etc. In case malware detects it's been run from a virtual machine, it lets execution stop analysis right away.

It proceeds with the attack if no virtual environment is detected. Here, it decodes more scripts, to which include a fake PDF and a batch file. These are stored in the victim's Downloads folder using seemingly innocent names such as "PositionApplied_VoyMedia.pdf."

Decryption and Execution Methods

Once the PowerShell script is fully executed, then decrypted strings from the "output.bat" file using hardcoded keys and decompressed through GZip streams. Then, it will produce a .NET executable running in the memory which will be providing further evasion for the malware against detection by antivirus software.

But the malware itself, also performs a whole cycle of checks to determine whether it is running in a sandbox or emulated environment. It can look for some known file names and DLL modules common in virtualized settings as well as measure discrepancies in time to detect emulation. If these checks return a result that suggests a virtual environment, then the malware will throw an exception, bringing all subsequent activity to a halt.

Once the malware has managed to infect a system, it immediately looks for administrative privileges. If they are not found, then it uses PowerShell commands for privilege escalation. Once it gains administrative control, it ensures persistence in the sense that it copies itself to a hidden folder inside the Windows directory. It also modifies the Windows registry so that it can execute automatically at startup.

Defence Evasion and Further Damage 

For the same purpose, the malware employs supplementary defence evasion techniques to go unnoticed. It disables Windows event tracing functions which makes it more difficult to track its activities by security software. In addition to this, it encrypts and compresses key components in a way that their actions are even more unidentifiable.

This last stage of the attack uses Quasar RAT. Both data stealing and long-term access to the infected system are done through the use of a remote access tool. This adapted version of Quasar RAT is less detectable, so the attackers will not easily have it identified or removed by security software.

This is a multi-stage malware attack against digital marketing professionals, especially those working in Meta advertising. It's a very sophisticated and dangerous operation with phishing emails, PowerShell commands combined with advanced evasion techniques to make it even harder to detect and stop. Security experts advise on extreme caution while handling attachment files from emails, specifically in a non-virtualized environment; all the software and systems must be up to date to prevent this kind of threat, they conclude.