- What is NanoCore malware?

NanoCore is a RAT. This malware is highly customizable with plugins that allow attackers to tailor its functionality to their needs. NanoCore is created with the .NET framework.

This malware was recorded in the wild for the first time in 2013. Since then it has become extremely popular. It is now used in attacks all around the world. As a modular malware, the functionality of the NanoCore backdoor can be greatly expanded with plugins. This makes an already dangerous RAT potentially even more destructive for the company's cybersecurity.

The accessibility, ease of use, and a bunch of information on NanoCore are still contributing to its growing popularity. It’s not completely certain whether the malware was being developed as a commercial program for institutions, or the creator had a goal to create malicious software from the beginning, Regardless, NanoCore author, Taylor Huddleston was tracked down and arrested by the FBI.

- How does NanoCore spread?

NanoCore RAT is distributed using multiple methods. However, the most commonly used is spam email campaigns. They trick users into downloading malicious documents, often presented as price lists or purchase orders.

The emails sometimes contain malicious attachments with .img or .iso extension. The large size of these files makes it difficult to scan them. Some versions of malware are also spread by a ZIP file which evades secure email gateways. Several file structure works here: one file script will download the payload while the rest are decoys that ensure the malicious content goes unnoticed by the system's security.

- NanoCore RAT execution process:

NanoCore is delivered to the victim’s PC using the AutoIt program. Not unlike Agent Tesla malware, which is somewhat typical for this type of RATs. Typically, NanoCore is spread using Microsoft Word documents. Infected files contain an embedded executable file or an exploit.

According to the RAT analysis, once the script file is opened an embedded macros download an executable script file and rename it. The downloaded executable file runs itself and creates a child process. The malware is able to use Regsvcs and Regasm to proxy the code execution through a trusted Windows utility.