The Russian cybercriminal group CryptoBytes has intensified its ransomware operations by using a modified version of the UxCryptor malware. Active since at least 2023, CryptoBytes primarily targets Windows systems worldwide, leveraging leaked ransomware builders to carry out their attacks. SonicWall’s Capture Labs team reports that the group uses sophisticated anti-analysis techniques designed to evade detection, making it more difficult for security researchers to track and analyze the malware. Additionally, the group employs psychological pressure tactics to intimidate victims into paying ransoms in cryptocurrency, further enhancing the effectiveness of their extortion campaigns.
The UxCryptor ransomware initiates its attack with three consecutive ransom screens, all written in Russian, which demand payment via Telegram and leave a persistent ransom note on the victim’s system. The .NET-based malware begins its destructive routine by forcibly terminating Windows Explorer using a taskkill command, effectively disabling the user interface while the malware runs in the background. This disruption allows the ransomware to carry out its attack unnoticed by the victim. The use of these techniques increases the ransomware’s ability to control the victim’s system and make recovery difficult.
In addition to these basic functions, UxCryptor employs advanced evasion techniques to avoid detection. The malware checks for sandbox environments using DLL fingerprinting and detects virtual machines through WMI queries, comparing the manufacturer and model strings to known virtualization platforms. It also terminates critical applications, such as Discord, Skype, Zoom, and web browsers, to prevent victims from communicating and seeking help. The ransomware also manipulates system registry values to prevent recovery tools from executing, ensuring that it remains persistent and continues its attack.
While the sample analyzed by SonicWall contained non-functional encryption routines, operational versions of UxCryptor use AES-256-CBC encryption with hardcoded keys to lock the victim’s files. The encrypted files are given the .ux-cryptobytes extension, making it easy for victims to identify the ransomware’s work. SonicWall’s Capture ATP and Capture Client solutions currently block UxCryptor variants using behavioral analysis signatures. Security experts recommend patching Windows systems promptly and implementing network segmentation to contain potential outbreaks. CryptoBytes is refining the capabilities of UxCryptor, with increasing attacks observed in SMBs across Eastern Europe, signaling the group’s growing threat.
