In Q3 2024, a significant rise in cyberattacks utilizing the Remcos remote access Trojan (RAT) has been detected. This RAT, typically delivered via phishing emails and malicious attachments, allows attackers to gain remote control over infected systems, steal sensitive data, and carry out espionage activities. Remcos RAT is particularly dangerous due to its ability to bypass traditional security measures, making it a preferred tool among cybercriminals. Researchers at McAfee Labs have identified two key variants of the malware, each employing unique techniques to evade detection and enhance its effectiveness.
The first variant of Remcos RAT uses a highly obfuscated PowerShell script activated by a VBS file. This script downloads additional files from command-and-control (C2) servers and injects malicious code into RegAsm.exe, a legitimate Microsoft executable. The use of multi-layer obfuscation helps the malware avoid detection by disguising its activity within legitimate system directories and paths. This makes it difficult for traditional security solutions to spot the malware during execution.
The second variant of Remcos RAT is spread through phishing emails that contain malicious Microsoft Office Open XML (DOCX) attachments. These files exploit the CVE-2017-11882 vulnerability, a remote code execution flaw, to download the malware payload once executed. Upon activation, the malware deploys Remcos RAT, allowing cybercriminals to establish remote access to the victim’s system. Both variants share several advanced techniques to avoid detection, including the use of Base64 encoding and reversed URLs to obscure their activities.
To ensure persistence, these Remcos RAT variants modify system registries and add entries to the startup folder, enabling them to remain active even after a system reboot. McAfee Labs has released indicators of compromise (IOCs) to aid in detection, including file hashes and URLs. With the threat of Remcos RAT on the rise, experts stress the importance of patching known vulnerabilities, implementing multi-layered security defenses, and educating users on how to recognize phishing attempts. By taking these proactive measures, organizations can significantly reduce their risk of falling victim to this persistent and evasive threat.
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