A campaign that has been active for the past few months has been leveraging compromised websites to spread fake software updates that in some cases delivered the NetSupport Manager remote access tool (RAT), FireEye reports.
A commercially available RAT, NetSupport Manager is employed by administrators for remote access to client computers. However, the legitimate application can also be abused by malicious actors who install it on victim computers without the owners’ knowledge, to gain unauthorized access to their machines.
For distribution, the actors abuse compromised websites and masquerade the RAT as fake updates for popular applications, including Adobe Flash, Chrome, and FireFox. Should the user accept the update, a malicious JavaScript file is downloaded, mostly from a Dropbox link.
The file collects basic system information and sends it to the server, receives additional commands from the server, and then executes a JavaScript to deliver the final payload. Named Update.js, the JavaScript that delivers the payload is executed from %AppData% with the help of wscript.exe, FireEye says.
The malware authors applied multiple layers of obfuscation to the initial JavaScript and attempted to make analysis harder for the second JavaScript file. By using the caller and callee function code to get the key for decryption, the attackers ensured that, once an analyst adds or removes anything from it, the script won’t retrieve the key and will terminate with an exception.
After initial execution, the JavaScript initiates the connection to the command and control (C&C) server and sends a value named tid and the current date of the system in encoded format. The script then decodes the server response and executes it as a function named step2.
This function collects various system information, encodes it and sends it to the server: architecture, computer name, user name, processors, OS, domain, manufacturer, model, BIOS version, anti-spyware product, anti-virus product, MAC address, keyboard, pointing device, display controller configuration, and process list.
The server then responds with encoded content: a function named step3 and Update.js, which downloads and executes the final payload.
The code leverages PowerShell commands to download multiple files from the server, including a 7zip standalone executable, a password-protected archive file containing the RAT, and a batch script to install the NetSupport client on the system.
The batch script was also designed to disable Windows Error Reporting and App Compatibility, add the remote control client executable to the firewall’s allowed program list, add a Run registry entry or download a shortcut file to Startup folder for persistence, hide files, delete artefacts, and execute the RAT. During analysis, the researchers noticed that the script was regularly updated by the malware.
With the help of NetSupport Manager, attackers could gain remote access to the compromised systems, transfer files, launch applications, get the system’s location, and remotely retrieve inventory and system information.
The final JavaScript also downloaded a txt file containing a list of IP addresses that the researchers say could be compromised systems. These IPs belong mostly to the U.S., Germany, and the Netherlands, but to other regions as well.
Related: Fake Chrome Font Update Attack Distributes Backdoor