eSentire White Logo

Security advisories | Feb 27, 2019

Increase in Emotet Infections

The eSentire Threat Intelligence team has observed an increase in successful Emotet infections coupled with lateral movement after the initial infection. eSentire Threat Intelligence assesses with medium confidence that the prevalence of infections will continue to rise given the current success of lateral movement and ease of delivery.

The initial infection vector is Microsoft Word documents downloaded from an embedded link inside fake invoice emails (Image 1). The trojan can spread through windows SMB file shares and is capable of downloading additional payloads from command & control servers. Samples observed employed randomly generated file names by victim asset and altered its file composition on disk at regular intervals to evade detection based on file hash.

Performing the mitigating actions listed below will significantly reduce the potential of Emotet infection and minimize the likelihood of successful lateral movement.

What we’re doing about it

  • The eSentire Threat Intelligence team is actively blocking IP addresses associated with Emotet
  • esENDPOINT detects the execution of malicious activity associated with Emotet
  • Signatures have been deployed on esNETWORK to detect connections related to Emotet Command and Control

What you should do about it

  • Conduct user awareness training around spam emails and suspicious documents
  • Implement the principle of least privilege to limit the chance of an attacker gaining administrative access. The malware requires local administrative access on the remote system in order to copy and execute from the $admin SMB share
  • Ensure the use of strong and unique passwords across the corporate environment
  • Disable macros from running within Microsoft Office documents
  • Software Restriction Policies (SRP) should be deployed in order to allow only known applications to run and prevent the execution of files from temporary directories
  • Ensure that Anti-Virus software conducts scans in regular and frequent intervals
  • Segregate networks and business functions
  • Perform out-of-band network management on critical devices
  • Block or restrict access to SMB file shares*

Additional information

Emotet has been active since 2014 and has incorporated various techniques to steal information from victims.

In the most recent Emotet campaigns, the threat actor(s) were found to be hosting documents on compromised domains. When the macro is executed a PowerShell command is used to retrieve an Emotet payload from another compromised domain. Lateral movement is then achieved by using the default $admin SMB file share across Windows machines. Depending on the infected user’s permission level, the threat actor(s) may configure persistence through registry run keys or a service.

Figure 1: Word Document that retrieves Emotet

[image src="/assets/advisories/255399da08/increase-in-emotet-infections.png" id="705" width="305" height="161" class="leftAlone ss-htmleditorfield-file image" title="increase in emotet infections"]

*Disabling or blocking SMB may create problems by obstructing access to shared files, data, or devices. Weigh the benefits of mitigation against potential disruptions to users.

Indicators of Compromise

File Names:

  • Overdue-payment-#######-########...
  • Invoice-##*####.doc

Current Persistence Mechanisms:

Local Admin Access:

Creates Service

Description: Duplicates description from an existing service

Directory of executable: c:\windows\syswow64\[Random Name].exe OR c:\windows\[Random Name].exe

Normal User:  

Registry Run Key

HKEY_CURRENT_USER\software\microsoft\windows\currentversion\run\[Random Name]