Hackers Employing Steganography Methods to Deliver Notorious RemcosRAT

Hackers are now using steganography techniques to distribute the notorious Remote Access Trojan (RAT) known as RemcosRAT.

This method, which involves hiding malicious code within seemingly innocuous image files, marks a concerning evolution in malware delivery tactics.

The Initial Breach: Word Documents and RTF Files

The attack begins with a seemingly harmless Word document that contains an external link.

This document employs a template injection technique designed to exploit vulnerabilities within the document’s processing.

The AhnLab Security Intelligence Centre (ASEC) has recently found that steganography is being used to spread RemcosRAT.

Hackers Employing Steganography Methods to Deliver Notorious RemcosRAT
A Word document containing an external link


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Upon opening the document, an RTF file is downloaded and executed.

This file exploits a known vulnerability in the equation editor component (EQNEDT32.EXE) of Microsoft Word, leading to the download of a VBScript with a misleading “.jpg” file extension from a command and control (C2) server.

Another VBScript is fetched from “paste.ee”, a service that allows users to upload and share text snippets.

VBScript downloaded by the RTF file
VBScript downloaded by the RTF file

The Steganography Technique

The downloaded VBScript is heavily obfuscated, making it difficult for traditional antivirus software to detect the malicious intent.

This script executes a PowerShell command, which further downloads an image from an external source.

The obfuscated script (eh1G4)
The obfuscated script (eh1G4)

The cunning aspect of this attack lies within the downloaded image file.

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The image contains Base64 encoded data hidden behind the “FF D9” marker, which typically denotes the end of a JPEG file. The PowerShell script locates the data encoded between “<<BASE64 START>>” and “BASE64_END” markers and decodes it.

The PowerShell script downloading a steganography image
The PowerShell script downloading a steganography image

The decoded data reveals a “.NET DLL” file, which is then executed through reflective code loading, a technique that allows code to be executed within the memory space of a process.

The Base64-encoded data contained in a normal image file
The Base64-encoded data contained in a normal image file

Final Execution: RemcosRAT Deployment

The script doesn’t stop there; it downloads an additional file from the C2 server and creates a RegAsm.exe child process to execute the file using the process hollowing technique.

This ultimately leads to the execution of RemcosRAT on the victim’s machine.

RemcosRAT executed through process hollowing
RemcosRAT executed through the process of hollowing

Given the diverse methods through which Remcos RAT can be distributed, including spam emails and disguised crack software download links, users are urged to exercise extreme caution.

Keeping antivirus solutions updated to the latest version is also recommended to block such malware infections preemptively.

This sophisticated use of steganography to conceal and deliver malware represents a significant shift in the landscape of cyber threats.

As attackers continue to innovate, the importance of maintaining robust cybersecurity practices and awareness among users cannot be overstated.

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Author: Divya