Remcos RAT (Remote Control and Surveillance) is a type of Remote Access Trojan used for unauthorized access and control of a computer system. 

It allows threat actors to perform various malicious activities like:-

• Spying
• Data theft
• Remote control of the infected system

Cybersecurity researchers at Uptycs recently discovered that the threat group UAC-0050 had been actively using the Remcos RAT pipe method for evasion to target Ukraine.

The threat actors have implemented this pipe method for interprocess communication.

UAC-0050 using RemcosRAT

Uptycs flagged a suspicious .lnk file on December 21, 2023, prompting cybersecurity researchers to investigate. 

They found UAC-0050 using RemcosRAT in a focused cyber operation against Ukrainian government agencies. 

The attack’s origin (likely phishing or spam emails) remains uncertain, but it posed as an IDF job offer to the Ukrainian military, aiming to infiltrate military networks through a sophisticated guise.

An LNK file initiates HTA download, containing a VBS script that triggers a PowerShell script to download word_update.exe. 

Launching word_update.exe executes cmd.exe, which shares the data through a pipe that leads to RemcosRAT in explorer.exe memory. 

The .lnk file, a Windows shortcut, is the investigation’s starting point. This case’s .lnk file checks antivirus info, which alters ‘the Windows Defender’ to avoid an ‘exit’ statement, and this ensures script continuity.

The .lnk file concludes with an obfuscated URL executed via MSHTA after deobfuscation. Researchers analyze the “6.hta” file that reveals a VBScript with fully obfuscated content. 

However, besides this, after deobfuscating the VBScript, a PowerShell script is uncovered.

Deobfuscation reveals $hQkGkZK, which leads to another PowerShell script with encoded data. Uptycs flags suspicious PowerShell activities that help in tracking payloads (word_update.exe, ofer.docx) from:-

The files land in “%appdata%,” and “word_update.exe” creates a self-copy with altered names. Meanwhile, the malware ensures persistence via the LNK file in startup, launching fmTask_dbg.exe at boot. 

Besides this, the fmTask_dbg.exe undergoes decryption that utilizes pipes to move data to cmd.exe by executing Remcos RAT.

The RemcosRAT is extracted from the cmd.exe memory and then decrypts the RC4-encrypted data in the payload’s Resource section using CyberChef.

Meanwhile, the identified Remcos version 4.9.2 Pro gathers the victim’s info, such as computer name and username.

From the following web browsers, the cookies and login data were removed by the RemcosRAT:-

• Internet Explorer
• Firefox
• Chrome

Recommendations

Here below, we have mentioned all the recommendations provided by the Uptycs researchers:-

• Make sure to enable sophisticated email filters for spam detection.
• Avoid clicking on links or opening attachments in identified spam emails.
• Use network monitoring tools to detect abnormal communication patterns.
• Regularly analyze and secure system configurations.
• Disable unnecessary services and startup entries.
• Closely monitor unnecessary services and startup entries.
• Ensure that behavioral analysis tools are employed to identify unusual activities.
• Detect and prevent attempts by RATs to establish persistence.