New Python-based Ransomware Poses as Locky
14.9.2018 securityweek Ransomware

A ransomware family used in attacks in July and August was posing as the infamous Locky ransomware that was highly active in 2016, Trend Micro researchers have discovered.

Written in Python and dubbed PyLocky, the new malware is packaged with PyInstaller, a tool that turns Python applications into standalone executables.

What makes PyLocky stand out from the crowd compared to other Python malware is anti-machine learning capability. It also uses the open-source script-based Inno Setup Installer and can pose a real challenge to static analysis methods, the security researchers say.

Furthermore, PyLocky has seen a highly concentrated distribution, with several spam emails targeting European countries, particularly France. Initially low, the spam volume increased in time.

A spam run observed in early August targeted French businesses, leveraging social engineering in an attempt to lure potential victims into clicking a link that redirects them to a malicious URL to download a ZIP file containing PyLocky.

Once installed on a victim’s machine, the malware attempts to encrypt image, video, document, sound, program, game, database, and archive files, among others. Overall, it targets a list of over 150 file types for encryption.

The ransomware abuses Windows Management Instrumentation (WMI) to check the properties of the affected system. It also features anti-sandbox capabilities, sleeping for 999,999 seconds (around 11.5 days) if the affected system has a total visible memory size of less than 4GB.

The ransomware’s encryption routines are implemented using the PyCrypto library and leverage the 3DES (Triple DES) cipher. PyLocky iterates through each logical drive, generates a list of files, and then overwrites targeted files with an encrypted version.

After completing the encryption process, PyLocky drops a ransom note and also establishes communication with its command and control (C&C) server. The malware’s ransom notes are in English, French, Korean, and Italian, suggesting that its operators are aiming at broader campaigns.

“PyLocky’s evasion techniques and abuse of legitimate tools typically reserved to administrators further exemplify the significance of defence in depth. For instance, machine learning is a valuable cybersecurity tool in detecting unique malware, but it is not a silver bullet. With today’s threats, there are different vectors at the attackers’ disposal, which makes a multi-layered approach to security important,” Trend Micro concludes.