A new EMOTET Trojan variant improves evasion techniques

Pierluigi Paganini November 18, 2017

Security experts at Trend Micro had recently observed a new variant of the EMOTET banking Trojan that implements new evasion features.

EMOTET, aka Geodo, is linked to the dreaded Dridex and Feodo (Cridex, Bugat)  malware families.

In past campaigns, EMOTET was used by crooks to steal banking credentials and as a malicious payload downloader.

The experts observed a re-emergence in the EMOTET activity in September, but the resents attacks present a few significant changes to elude sandbox and malware analysis.

“Based on our findings, EMOTET’s dropper changed from using RunPE to exploiting CreateTimerQueueTimer.” states Trend Micro.

The CreateTimerQueueTimer is a Windows application programming interface (API) that creates a queue for lightweight objects called timers that 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,” continues Trend Micro.

Other malware already abused this Windows API, such as the Hancitor banking Trojan and VAWTRAK.

The anti-analysis functionalities implemented by the latest variant allow to check when the scanner monitors activities in order to evade the detection.

CreateTimerQueueTimer allows EMOTET do the job every 0x3E8 milliseconds, the malware can determine if it runs in a sandbox environment and terminates its process if it does.

“This variant has the ability to check if it’s inside a sandbox environment at the second stage of its payload. The EMOTET loader will not proceed if it sees that it’s running inside a sandbox environment.” continues the analysis.

The dropper checks us the NetBIOS’ name is TEQUILABOOMBOOM, the UserName, and for the presence of specific files on the system.

If it does not have admin privileges, it creates an auto start service to maintain persistence on the infected machine, 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.

The new EMOTET variant is distributed via phishing messages containing a malicious URL used to drop weaponized document.

Trend Micro also published the Indicators of Compromise (IoCs) for the latest version of the malware.

Further details on the EMOTET C&C infrastructure were published by the popular security researcher MalwareTech (Marcus Hutchins).

“Using hacked websites to proxy C2 servers has become much more common because it adds a layer of protection preventing researchers from easily finding and shutting down the actual C2 server; furthermore, it’s hard for security companies to flag the servers as malicious when they’re actually legitimate websites which have been running for years, not new servers set up with domains bought the day before.” wrote MalwareTech.

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Pierluigi Paganini 

(Security Affairs – EMOTET, banking Trojan)

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