Emotet Malware Makes a Comeback with New Evasion Techniques

Since its inception, Emotet has continued to steadily evolve, adding new techniques for evasion and increasing its likelihood of successful infections. It is also able to host an array of modules, each used for different aspects of information theft that report back to their command-and-control (C2) servers. From process monitoring to grabbing Microsoft® Outlook® email addresses, Emotet has been observed to inject both proprietary modules and readily available freeware tools, adding and tweaking them over the years with alarming effectiveness. More recently, Emotet has added a new Server Message Block (SMB) spreader module, used as an effective method for lateral movement once placed on a target machine.

The SMB spreader starts this process by gaining the same security privileges as the initial target account. Once loaded onto a victim’s system, this module begins impersonating that user by duplicating their account token via the SecurityImpersonation level. This gives a process the same privileges as the current user on that system. With these duplicated privileges, the spreader calls a function “ImpersonateLoggedOnUser” to perform actions in the same security context of the account that is currently logged in.

From here, the module begins enumerating network resources using the WinAPIs WnetOpenEnumW and WnetEnumResourceW. Of these resources, it saves any potential remote servers to a list. Then, using two additional hardcoded lists (one of common usernames, another of common passwords), the spreader will iterate over this list of server names and begin bruteforcing the IPC$ share with the WinAPI WNetAddConnection2W in hopes of a successful connection.

If no connection is made with the credentials at hand, the SMB spreader can also attempt to seek additional usernames from the server being targeted with the NetUserEnum WinAPI. Any potential new usernames found will also be bruteforced with the hardcoded list of passwords to login to the IPC$ share.
If a connection succeeds, the spreader finally attempts to connect to either the ADMIN$ and C$ shares. From there, it finally copies the Emotet loader to said share and launches it as a service. The service executes with regsvr32.exe, and lateral movement is achieved.

Along with the SMB spreader, another recently added module is used to target a victim’s Google Chrome browser in the hopes of stealing stored credit card information.
To load some of its previously used modules, Emotet has been observed to use an injection technique known as Heaven’s Gate. Made popular in the mid-2000s, Heaven’s Gate is an infamous method used by malware to bypass Windows® on Windows64 (WoW64) API hooks, by taking malicious 32-bit processes to inject into 64-bit processes. This technique works because while many security products monitor file activity by hooking 32-bit APIs (CreateFile, WriteFile, OpenFile), when running 64-bit code, an opportunity is presented to completely bypass many system calls which would render the malicious code segments far too noisy.

With the newest wave of Emotet spam emails, the attached .xls files have a new method for tricking users into allowing macros to download the dropper. In addition to this, new Emotet variants have now moved from 32bit to 64bit, as another method for evading detection.