Emotet Malware’s New Evasion Technique Lets Hacked Device Used as Proxy command and control (C&C) servers

by chebbi abir

A new wave of Emotet malware using a special type of evasion technique to fool the security software and hide the POST-infection traffic and evade the detection.

Also it initially uses the hacked devices as proxy command and control (C&C) servers and redirects the traffic to the original C&C server that operating by threat actors.

Emotet is one of the notorious malware family that infects various victims around the would and the operator behind this malware earned millions of Dollars.

Researchers says that the traffic is very complex to analyse due to various evasion technique that is being used during the malware development phase.

Emotet malware is being used to compromise and collect vulnerable connected devices, which could become resources for other malicious purposes.

Emotet malware infection Process

Initially, a spam email campaign that contains an attached malicious invoice file and body of the email tricks users into downloading malicious files.

Attached zip is files actually password protected which required users to obtain the password from the body of the email and use it to open the file.

“A look into the ZIP file shows that it contains variants of Powload (detected as Trojan.W97M.POWLOAD). If the user enters the password, the file uses Powershell to download an executable file, which is Emotet’s payload.”

A post infection traffic contains a randomized number used as a URI directory path that helps the malware evade network-based detection.

New Emotet post-infection HTTP Post request traffic

The previous version of Emotet malware used an HTTP GET request to send victim information to the C&C server and the stolen data store in the cookie header.

Comparison between the new Emotet C&C traffic and the previous Emotet C&C traffic

But this new wave Actors stayed away from using the Cookie header and changed the HTTP request method to POST. The data is still encrypted with an RSA key and AES, and encoded in Base 64.

According to Trend Micro Research, “Investigating some of the most recent live IP addresses of known Emotet C&C servers, we saw that they were actually different types of connected devices: One is the web interface of the router, another is an embedded server for managing printers and other devices “

This new campaign was observed since March and its clear that the connected devices are used for the additional layer of command & controls server communication.

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