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EMOTET Trojan Variant Evades Malware Analysis

A recently observed variant of the EMOTET banking Trojan features new routines that allow it to evade sandbox and malware analysis, Trend Micro security researchers say.

A recently observed variant of the EMOTET banking Trojan features new routines that allow it to evade sandbox and malware analysis, Trend Micro security researchers say.

Also known as Geodo, EMOTET is a piece of malware related to the Dridex and Feodo (Cridex, Bugat) families. Mainly used to steal banking credentials and other sensitive information, EMOTET can also be used as a Trojan downloader, and recent attacks have dropped various malicious payloads.

In a report published in early November, Microsoft revealed that EMOTET has been increasingly targeting business users.

According to Trend Micro, EMOTET’s dropper changed from using RunPE to exploiting a Windows application programming interface (API) called CreateTimerQueueTimer. The API creates a queue for lightweight objects called timers, which are meant to enable the selection of a callback function at a specified time.

“The original function of the API is to be part of the process chain by creating a timer routine, but here, the callback function of the API becomes EMOTET’s actual payload. EMOTET seems to have traded RunPE for a Windows API because the exploitation of the former has become popular while the latter is lesser known, theoretically making it more difficult to detect by security scanners,” Trend Micro explains.

EMOTET, however, is not the first malware family to abuse this Windows API, as the Hancitor banking Trojan that also dropped PONY and VAWTRAK used it in its dropper (a malicious macro document) as well.

The new Trojan variant also features an anti-analysis technique that involves checking when the scanner monitors activities in order to dodge detection. With the use of said Windows API, the malware can do the job every 0x3E8 milliseconds, the security researchers say.

At the second stage of the payload, the new Trojan variant can check if it runs inside a sandbox environment and terminates its process if it does. The dropper checks the NetBIOS’ name, the UserName, and for the presence of specific files on the system.

The malware also runs itself through another process if it does not have admin privilege. If it does have said privileges, it creates an auto start service for persistence, renames it and starts it, collects system information, encrypts it, and sends it via a POST request to the command and control (C&C) server.

In a recent analysis of the EMOTET C&C infrastructure, security researcher MalwareTech (Marcus Hutchins) notes that the threat is using hardcoded IP addresses to connect to the server. However, it uses compromised sites as proxies for the C&C connection.

This practice, the researcher says, has become increasingly popular “because it adds a layer of protection preventing researchers from easily finding and shutting down the actual C2 server.” It also makes it difficult to flag the servers as malicious, given that they are legitimate websites that have been running for years.

The new EMOTET variant is distributed via phishing emails containing a malicious URL meant to drop a macro-enabled document. Best practices for defending against phishing attacks should keep both enterprises and end-users safe from the threat, Trend Micro notes.

Related: Qakbot, Emotet Increasingly Targeting Business Users: Microsoft

Related: Network Spreading Capabilities Added to Emotet Trojan

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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