A new attack vector utilizing XenoRAT, an open-source remote access tool, has been discovered, leveraging Excel XLL files to bypass traditional security measures. Researchers at Hunt uncovered this technique, highlighting how attackers disguise the malicious files as “Payment Details” to trick users into execution. These XLL files, created using the Excel-DNA framework, enable the malware to load compressed .NET assemblies directly into memory, avoiding detection by many conventional tools.
The attack follows a multi-stage process, starting with the execution of the disguised XLL file. This triggers an obfuscated batch file, extracts an SFX RAR archive, and displays a decoy PDF to maintain the illusion of legitimacy. Security analysts noted the use of ConfuserEx for obfuscation, complicating analysis, and detected an anomalous timestamp (10/22/2052) to evade automated detection systems. The malware’s command-and-control (C2) server communicates over TCP port 1391 and is hosted in Bulgaria, with additional monitoring potential via a self-signed certificate on the RDP port.
XenoRAT, previously known for targeting gamers through spearphishing and counterfeit software, has now expanded its scope. This evolution demonstrates the adaptability of threat actors, who exploit less common file extensions like XLL to infiltrate systems undetected. The sophisticated delivery and execution methods employed underline the increasing complexity of malware campaigns targeting both individuals and organizations.
To combat these threats, security professionals are advised to implement stricter monitoring of uncommon file types, enhance detection mechanisms for obfuscated malware, and maintain regular patching and updates. The discovery of this advanced attack vector underscores the importance of vigilance and proactive defense measures as threat actors continue to refine their tactics to bypass security systems.
