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Pyarmor Pro upgrade boosts Batloader malware’s stealth capability

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Water Minyades, a notorious cybercriminal group behind the Batloader initial access malware, has upgraded it significantly, introducing more sophisticated measures to obfuscate the malicious Python scripts.

The latest enhancement in Batloader’s evasion strategy involves the utilisation of Pyarmor Pro, an advanced iteration of the Pyarmor protector command-line tool, as discovered by the researchers at Trend Micro. This upgraded version poses a formidable challenge to cybersecurity analysts and software, as it intricately conceals the core malicious scripts, making de-obfuscation considerably more intricate.

Water Minyades’ shift to Pyarmor Pro is a strategic manoeuvre to elude cybersecurity measures, particularly those of antivirus engines, which often lack an effective unpacked engine for Pyarmor. This deficiency adds a layer of complexity to identifying and neutralising these nefarious scripts, emphasising the need for heightened vigilance in cybersecurity.

Batloader’s evasion tactics extend beyond Pyarmor Pro, encompassing an array of methods aimed at thwarting detection and analysis. A noteworthy example includes utilising large MSI files as a vehicle for malware delivery. These files, laden with malicious intent, are intricately designed to evade security protocol and infiltrate systems. Coupled with this, Batloader employs custom action scripts to initiate its kill chain, exemplifying the malware’s multi-faceted approach to compromise.

Pyarmor script. | Source: Trend Micro

Upon analysing Batloader’s modus operandi, the researchers unveiled the intricacies of its execution chain. The malware meticulously checks for administrative privileges on the victim’s machine. If absent, it triggers a User Account Control (UAV) prompt, ensuring it gains the necessary access.

Subsequently, Batloader silently installs WinRAR using a disguised installer, paving the way for further stages of the attack. The malware’s evasion techniques are strategically aimed at bypassing security measures, enabling it to function undetected.

Python2.bat file that triggers the User Account Control prompt. | Source: Trend Micro

As Water Minyades continues to evolve Batloader’s evasion strategies, the cybersecurity community faces an escalating challenge in combatting this threat. The sophisticated tactics employed, ranging from obfuscated Python scripts to strategic infiltration techniques, highlight the relentless pursuit of cybercriminals to exploit vulnerabilities.

Batloader was identified by Trend Micro as Trojan.Win32.BATLOADER, representing an initial access malware lineage recognized for using malvertising strategies. This malware variant employs script-based malicious software concealed within Microsoft Software Installation (MSI) packages, often distributed via seemingly genuine yet malicious websites.

Earlier this year, Mandiant researchers uncovered Batloader’s engagement in search engine optimization (SEO) poisoning tactics as part of its attack methodology.

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Kumar Hemant

Deputy Editor at Candid.Technology. Hemant writes at the intersection of tech and culture and has a keen interest in science, social issues and international relations. You can contact him here: [email protected]