New Emotet Trojan Feature Spreads Malware on Internal Networks

Researchers at Fidelis Cybersecurity recently observed a new variant of the Emotet Trojan. According to the company’s Threatgeek blog, this variant contains a feature that can help the malware propagate over internal networks.

SecurityWeek noted that the success of this network-spreading feature may encourage other threat actors to use similar components in their malware.

Emotet Trojan Tracks Geographic Spread of Malware

Previously, Emotet was used as a banking Trojan that targeted users in Europe and the U.S. But Fidelis noticed that in recent attacks, a new variant served as a downloader for other Trojans based on the victim’s geographic location.

Here’s how it works: The spreader enumerates a network’s resources and seeks out shares to which it can write a file and create a remote service, which is called Windows Defender System Service. According to the security firm, for any shared password-protected resource the malware finds on the network, it tries to brute-force user and administrator accounts for IPC$.

After a few checks, the Trojan attempts to connect to the IPC$ share. If it’s unable to connect, it tries to derive the normal user accounts using NetUserEnum. Using the derived list of usernames, it then attempts to brute-force the passwords for each user with an onboard password list in a dictionary-style attack. If this works, it forms the basis of what actually gets loaded into the remote computer.

The remote service is what actually writes the malware to the shared resource. It then executes it, making a callout to a hardcoded IP. Because the victim’s computer name is used in the POST request data, malware actors can quickly track statistics on locations to which the Trojan has spread.

Spreader Feature Is Distinct From Emotet Malware

Researchers drew attention to differences between Emotet packaging, which is usually encrypted, as well as the spreader feature. These differences suggest that the spreader may be a test package produced by a specific actor rather than Emotet itself.

In any case, it is more than prudent to stop this threat at the injection point, which is a phishing email. To stop the spread of Trojans, practice caution by not opening unverified emails or attachments. These standard defenses that security professionals recommend may end up saving the user from financial harm.

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Larry Loeb

Principal, PBC Enterprises

Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other...