CRON#TRAP Malware Evades Antivirus via Linux VM Infection

New Malware Campaign CRON#TRAP Targets Windows Systems with Linux Backdoor

Cybersecurity experts have identified a concerning new malware campaign, codenamed CRON#TRAP, that infects Windows systems by deploying a Linux virtual instance equipped with a backdoor. This sophisticated technique grants attackers remote access to compromised hosts, raising alarms in the cybersecurity community. The CRON#TRAP campaign primarily spreads through phishing emails containing malicious Windows shortcut (LNK) files, which are typically disguised in ZIP archives.

Researchers from Securonix, Den Iuzvyk and Tim Peck, highlighted the alarming nature of this campaign, stating, "The emulated Linux instance comes pre-configured with a backdoor that automatically connects to an attacker-controlled command-and-control (C2) server." This allows cybercriminals to maintain an undetected presence on the victim’s machine, facilitating further malicious activities in a concealed environment that eludes traditional antivirus detection.

How the CRON#TRAP Campaign Operates

The CRON#TRAP campaign employs a multi-faceted approach to execute its attack:

• Phishing Emails: The campaign originates from phishing messages that masquerade as an "OneAmerica survey." These emails contain a sizable 285MB ZIP archive, which, when opened, initiates the infection process.
• Malicious Shortcut: The LNK file within the ZIP archive extracts and launches a lightweight, custom Linux environment via Quick Emulator (QEMU), an open-source virtualization tool running on Tiny Core Linux.
• Background Execution: Upon running, the shortcut triggers PowerShell commands that re-extract the ZIP file and execute a hidden "start.bat" script. This script presents a fake error message to the victim, creating the illusion that the survey link is inactive while secretly setting up the QEMU virtual Linux environment.

The Role of Chisel in the Attack

Once the QEMU instance is operational, it utilizes a pre-configured Chisel tunneling utility, allowing attackers to establish remote access immediately. According to researchers, “The binary appears to be a pre-configured Chisel client designed to connect to a remote Command and Control (C2) server.” This functionality effectively transforms the Chisel client into a full backdoor, enabling bidirectional command and control traffic flow.

Evolving Threat Landscape

The CRON#TRAP campaign is part of a broader trend of evolving tactics used by threat actors. For instance, a spear-phishing campaign has been reported, targeting electronic manufacturing, engineering, and industrial firms in European countries to deliver the evasive GuLoader malware.

• Targeted Industries: This malicious effort has predominantly affected organizations in Romania, Poland, Germany, and Kazakhstan.
• Execution Method: The attack begins with a batch file embedded in an archive, which runs an obfuscated PowerShell script to download additional malicious payloads.

Cado Security researcher Tara Gould emphasizes the need for heightened security measures, stating, "Guloader malware continues to adapt its techniques to evade detection to deliver RATs." The ongoing resilience of these threats underscores the importance of proactive cybersecurity strategies.

Conclusion: Protect Your Systems

As malware campaigns like CRON#TRAP and GuLoader evolve, organizations must remain vigilant. Implementing robust security protocols and training employees to recognize phishing attempts can significantly reduce the risk of infection.

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