Ostap

Recently, cybersecurity researchers spotted the activity of a JavaScript-based Trojan Downloader called the Ostap Downloader. This Trojan downloader appears to have been used to propagate the Trickbot malware. The Ostap Trojan Downloader is capable of detecting and avoiding any anti-virus tools and services which may be present on the compromised system. It is also meant to examine the infected PC and collect information. If the Ostap Downloader is satisfied with the data collected, it will proceed the attack by establishing a connection with the C&C (Command & Control) server of its operators. The Ostap Trojan Downloader will then proceed to grab the malicious payload it is meant to distribute from the attackers' C&C server and deploy it on the compromised machine. So far, it appears that the Ostap Downloader has only been used in combination with the Trickbot Trojan, but this does not mean that the operators of this threat will not use it to spread other types of malware in the future.

State-of-the-Art Obfuscation Techniques

Most downloaders utilize PowerShell consoles that execute a VBA script, which triggers the download and initialization of the final payload. This is not the case with the Ostap Trojan Downloader as this threat is entirely written in the JavaScript programming language. Furthermore, the obfuscation methods used in the Ostap Downloader are state-of-the-art tier. The creators of the Ostap Trojan Downloader have added up to 36,000 fake code lines to make it nearly impossible to detect or dissect. In reality, the code lines which are significant are probably not more than a dozen among tens of thousands of bogus code lines making it extremely difficult to dig through all the junk to get to the significant parts.

Propagation Method

The propagation method used in the spreading of the Ostap Trojan Downloader is phishing email campaigns. These fraudulent emails appear a purchase notices that have '. DOCM' files attached to them which carries the macro-script needed to spread this threat. Once the user opens the file, the JavaScript file that is carrying the Ostap Trojan Downloader will be triggered. Then, the Ostap Downloader will check if it has landed on a regular system or a sandbox environment. The Ostap Trojan Downloader is also able to stay under the radar of most anti-malware applications because of its obfuscated code.

You should be very careful when opening email attachments as they are often used to propagate malware. Also, make sure you download and install a legitimate anti-malware application which will keep your system secure.