IBM X-Force researchers have discovered a new campaign targeting organizations with fake business emails that deliver NetWire remote-access Trojan (RAT) variants.

The RAT is hidden inside an IMG file, which is a file extension used by disk imaging software. Since many attachments can be automatically blocked by email security controls, spammers often carefully choose the type of file extensions they use in malspam messages, and shuffle the types of files they conceal malware in. X-Force’s analysis shows that emails delivered by the NetWire RAT in this campaign are being sent from a small number of unique senders supposedly located in Germany.

The NetWire RAT is a malicious tool that emerged in the wild in 2012. This multi-platform malware has since undergone various upgrade cycles and was detected in different types of attacks that range from cybercrime endeavors by Nigerian scammers to advanced persistent threat (APT) attacks. The NetWire RAT is a commercial offering that can be easily purchased on Dark Web markets, which means that it can be used by just about any threat actor.

This isn’t the first time NetWire is being delivered in fake business communications. In a previous campaign launched in September 2019, its operators sent booby-trapped fake PDF files to potential victims, indicating it was a commercial invoice. The actual file was an executable that installed the NetWire RAT as soon as the file was clicked.

Extracting a RAT

In one of the samples we looked into, an IMG file named “Sales_Quotation_SQUO00001760.img.” was a way for the attackers to archive the malware until the file was clicked open. Once opened, it extracted an executable: the NetWire RAT.

Immediately after this initial execution, the malware established persistence via a scheduled task, a common tactic to many malware developers. Scheduled tasks enable the malware to keep checking that it’s active or relaunch itself in a recurring fashion.

Additionally, registry keys are created to store the command-and-control (C&C) server’s IP address and save data used by the malware to operate on the infected device. Communication with the C&C server is performed over TCP port 3012.

What’s the NetWire RAT Up To?

Since this malware can be used by any group with any motivation, attribution is rather futile. What we did want to figure out was what the NetWire RAT campaign we detected was after this time.

Looking at some unencrypted strings found in memory, we identified a series of strings written in a foreign language, which appears to be Indonesian. Below is a screenshot from Google Translate showing a rough translation of the various identified strings. Many of these terms either relate to a login prompt, payment options, donations or the term “afterlife savings”:

Figure 1: Translated malware strings from recent NetWire RAT campaign

This term may relate to permanent life insurance for retirement purposes offered in some parts of the world.

From the overall look of it, this campaign is financially motivated and most likely being carried out by local fraudsters looking to rob account owners in various ways. Although we have not seen the complete post-infection flow, it may be followed up by a 419-type scam, or might also include social engineering or phishing pages to lure the victim to enter their banking credentials and enable the attackers to take over their accounts.

Recent campaigns in the wild show that the NetWire RAT is not the only malware being delivered via disk imaging file extensions. This was somewhat of a trend in late 2019, likely because the same spamming operators were distributing RATs for different threat actors.

Commercial Malware Abounds

Oftentimes, as security professionals, we hear about the larger and more impactful data breaches, ransomware attacks, and destructive campaigns, which are often carried out by sophisticated cybercrime gangs. But while most financially motivated cybercrime is the work of larger, organized crime groups, smaller factions are still very much in business, and they too target businesses to compromise bank accounts and steal money by using commercially available malware year-round.

Indicators of compromise (IoCs) and other information on how to protect networks from the NetWire RAT can be found on IBM X-Force Exchange.