Security researchers discovered a new variant of the Emotet malware family that employed a wireless local area network (WLAN) as its distribution method.

Binary Defense spotted this WLAN distribution method in a self-extracting RAR file containing two binaries. First, it used “worm.exe” as a setup file to prepare its Wi-Fi spreading activity. The executable analyzed by researchers contained a timestamp of April 16, 2018, which would suggest that attackers have been spreading Emotet via Wi-Fi for close to two years. Even so, Binary Defense’s data indicated that Emotet might not drop its worm.exe binary too frequently.

The campaign leveraged worm.exe to enumerate all Wi-Fi devices enabled on the local computer and to profile all existing Wi-Fi networks. At that point, it launched into its brute-forcing connection loops to try to connect to a network, enumerate all devices and brute-force passwords for all users. When successful, the campaign moved to “service.exe,” a binary that it used to create a connection with its command-and-control (C&C) server and ultimately drop an embedded Emotet executable.

A Look Back at Emotet’s Recent Activity

The attack described above is one of the latest episodes in Emotet’s ongoing evolution. In December 2019, for instance, Cisco Talos witnessed a surge of activity in which the malware family used emails to target individuals in the U.S. military and government. In February 2020, IBM X-Force reported that malicious actors used SMS messages to masquerade as banks in an attempt to deliver Emotet.

How to Defend Against WLAN Distribution Tactics

Security professionals can help defend against malware campaigns that use WLANs for distribution by changing the default passwords on their routers and enabling multifactor authentication (MFA) whenever possible. Given Emotet’s frequent use of malicious email attachments as an infection vector, infosec personnel should also implement proper logging with their security information and event management (SIEM) team to monitor for the activation of malicious macros.

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