Remcos RAT

Adversaries don’t work 9-5 and neither do we. At eSentire, our 24/7 SOCs are staffed with Elite Threat Hunters and Cyber Analysts who hunt, investigate, contain and respond to threats within minutes.

We have discovered some of the most dangerous threats and nation state attacks in our space – including the Kaseya MSP breach and the more_eggs malware.

Our Security Operations Centers are supported with Threat Intelligence, Tactical Threat Response and Advanced Threat Analytics driven by our Threat Response Unit – the TRU team.

In TRU Positives, eSentire’s Threat Response Unit (TRU) provides a summary of a recent threat investigation. We outline how we responded to the confirmed threat and what recommendations we have going forward.

Here’s the latest from our TRU Team…

What did we find?

• Remcos (Remote Control & Surveillance Software) was identified in a customer environment in the legal services industry.
• Remcos is a malicious remote access tool (RAT) marketed as a legitimate remote administration tool which can be purchased for between €58-399.
  • The tool can be used to control the system, capture keystrokes, webcam images, screen captures, and passwords (among other capabilities).
  • Version 3.3.2 Pro was identified in this incident.
• The infection vector for Remcos was a password-protected, macro-enabled Excel file named “remittance advice.xlsm”.
  • Once opened, PowerShell is executed to retrieve a remote script (edi.vbs/firewall.vbs) from hxxp://lbl[.]support.
  • The script fetches additional components, enables persistence via registry run key and ultimately executes Remcos within a legitimate Windows process.

Figure 1 Online purchasing form for Remcos

Figure 2 Process tree showing execution stages

How did we find it?

• BlueSteel, our machine-learning powered PowerShell classifier, identified PowerShell commands executed by Remcos RAT
• MDR for Endpoint identified secondary execution phases.

What did we do?

• Our team of 24/7 SOC Cyber Analysts isolated the host and worked with the customer to remediate.

What can you learn from this TRU positive?

• Remcos provides an attacker with nearly full control of the compromised system, so rapid identification and removal is critical.
• Remcos stores captured information in the following files and folders:
  • %APPDATA%\rem\logs.dat (captured keystrokes)
  • %APPDATA%\Screenshots
  • %APPDATA%\MicRecords
• Unfortunately, antivirus detection for the macro-enabled Excel document is minimal since password-protected documents can be used to evade link and attachment inspection.
  • As of January 18th, 2022 only two vendors have identified it on VirusTotal.

Recommendations from our Threat Response Unit (TRU) Team:

• Employ email filtering and protection measures.
  • Block or quarantine email attachments such as EXEs, Password-Protected ZIPs, Javascript, and VisualBasic scripts.
  • Implement anti-spoofing measures such as DMARC and SPF.
  • Employ an MFA solution to reduce impact of compromised credentials.
  • Train users to identify and report suspicious emails.
• Protect endpoints against malware
  • Ensure antivirus signatures are up-to-date.
  • Use a Next-Gen AV (NGAV) or Endpoint Detection and Response (EDR) product to detect and contain threats.
  • Limit or disable macros across the organization. See UK's National Cyber Centre guidance on Macro Security.

Ask Yourself…

• Can my team prevent emails containing encrypted malicious documents from reaching users?
• Does my team have endpoint monitoring in place to identify malicious documents which bypass email controls?

Indicators of Compromise

If you’re not currently engaged with a Managed Detection and Response provider, we highly recommend you partner with us for security services in order to disrupt threats before they impact your business.

Want to learn more? Connect with an eSentire Security Specialist