How to Respond to Emotet Infection (FAQ)

Since October 2019, there has been a growing number of Emotet infection cases in Japan. JPCERT/CC issued a security alert as follows:

Alert Regarding Emotet Malware Infection
https://www.jpcert.or.jp/english/at/2019/at190044.html

The purpose of this entry is to provide instructions on how to check if you are infected with Emotet and what you can do in case of infection (based on the information available as of December 2019). If you are not familiar with the detailed investigation methods described here, it is recommended that you consult with security vendors who can assist you.

We have been informed of emails impersonating someone. What can we do?

When suspicious email impersonating someone with an attachment is received, it is possible that either of the following events has occurred:

A) The device that uses the sender’s account is infected with Emotet, and information about emails and contact list have been stolen.

B) Partners and users (with whom you have exchanged emails) have been infected with Emotet, and their contact list has been stolen. (The recipients of the malicious email have not been infected with Emotet, but the email address has been added to the lists of recipients.)

If the email referring to an actual message body (Figure 1) is received, the device that uses the sender’s email account is likely to be infected (case A).

Figure 1:Example of Emotet email in reply to an existing thread (A)

In case of an email as in Figure 2, it is assumed that the email is auto-generated to disguise itself as a reply to a thread. Both A) and B) can apply to this case, and it is unclear whether the device that uses the email account is infected or not.

Figure 2:Example of email disguising as a reply (B)

What can we do to check whether we are infected with Emotet or not?

1. Confirm with the impersonated person

Check whether the person opened the suspicious attachment and saw the messages in the sample screenshots (See Reference “The screenshots of the attached Word file”). If they have seen one of the messages, check whether the macro is enabled on their device. If the macro is enabled, it is possible that the device is infected with malware.

2. Perform the scan with anti-virus software

Perform device scan with the latest anti-virus signatures.
*Emotet has many variants, and even the latest signatures may not be able to detect infection for a few days. No detection does not necessarily mean no infection. It is recommended to update the signatures and conduct the scan regularly.

3. Check auto-start settings

Emotet has several methods for maintaining persistence such as setting auto-start registry keys, save the payload into Startup folder, etc.
Check the following settings and confirm that suspicious file or setting does not exist.

[Typical Windows OS auto-start settings]

  • Auto-start registry [*1]
  • Task Scheduler
  • Service
  • Startup folder

(*1)  HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run

[Folders that Emotet is likely to be located]

  • Folders under C:\Users(username)\AppData\Local\
  • C:\ProgramData\
  • C:\Windows\system32\
  • C:\
  • C:\Windows
  • C:\Windows\Syswow64

*If there is a suspicious executable file under C:\ProgramData\ that is registered in the Task Scheduler, it is likely that the device is also infected with Trickbot.

Figure 3: Example of Emotet registered in the Auto-start Registry [*1]
(*Folder names and executable file names are randomly created for each device.)

4. Check email server log

Check the following points in your email server logs:

  • High volume of impersonating emails whose HeaderFrom and EnvelopFrom do not match
  • Unusual increase in the volume of outbound emails
  • High volume of emails with a Word file attachment
5. Check network traffic log

If you record/monitor outbound communication, check proxy and firewall logs for any suspicious access to multiple ports (C&C server) from a single device.

[Example of ports that Emotet uses]

20/TCP, 22/TCP, 80/TCP, 443/TCP, 446/TCP, 447/TCP, 449/TCP,465/TCP, 7080/TCP, 8080/TCP, 8090/TCP etc.

Figure 4:C&C communication by Emotet (*Destination IP differs by sample)

What can we do when we find Emotet infection?

1. Isolate the infected device, preserve evidence and investigate affected area
  • Preserve evidence of the infected device
  • Check the emails stored in the device and email addresses in the contact list (These may have been leaked)
2. Change password of email accounts etc. used in the infected device
  • Email accounts used in Outlook and Thunderbird
  • Credentials stored in Web browsers
3. Investigate all devices in the network to which the infected device was connected
  • Check other devices in the network as the malware is capable of spreading infection by lateral movement
    • The following TTPs have been confirmed for lateral movement:
      • Leverage SMB vulnerability (EternalBlue)
      • Log on to Windows network
      • Use Administrative share
      • Register services
4. Monitor network traffic log
  • Make sure that the infected device is isolated and check whether there is any other infected device
5. Check other malware infection
  • Check whether the infected device is also infected with other types of malware as Emotet is capable of infecting the device with other types of malware. If this happens, further investigation and response is required.
    • Some victims in Japan have also been infected with banking trojans such as Ursnif and Trickbot
    • Victims overseas were also found infected with targeted ransomware
6. Alert stakeholders who may also be affected (whose email addresses have been stolen by the attacker)
  • Emails and email addresses in the contact list in the case A
    • Issue a press release if a wide range of stakeholders may be affected.
7. Initialise the infected device

How can we stop emails being sent from stolen accounts?

If emails and email addresses are stolen as a result of Emotet infection, impersonating emails with a malicious attachment will be sent continuously. Information of the stolen email addresses (message body and contact lists) are collected in the attack infrastructure, and this is used to distribute malware-attached emails. There is no way to stop emails from being sent.

It is likely that the recipients will continue to receive malware-attached emails repeatedly or impersonating emails will be sent to the stolen contacts. Please beware not to open suspicious email attachments. It is also recommended to perform the scan with the latest anti-virus signatures and make sure that your OS and software are running with the latest security updates.

What impact is expected if a device is infected with Emotet?

Emotet infection leads to exfiltration of emails and email addresses. Credentials stored in Web browsers can be harvested. It is also possible that the infection spreads to other devices in the network and that devices are at the risk of being infected with other types of malware such as banking trojans and ransomware.

What can we do to prevent Emotet infection?

Please refer to JPCERT/CC’s security alert for details.

Alert Regarding Emotet Malware Infection
https://www.jpcert.or.jp/english/at/2019/at190044.html

(Reference) “The screenshots of the attached Word file”

Since October 2019, the following 6 types of Word files leading to Emotet infection have been observed.

Figure 5: Attached file example 1 (since 2019/11/26)

 Figure 6: Attached file example 2 (since 2019/10/30)

 Figure 7: Attached file example 3

 Figure 8: Attached file example 4

 Figure 9: Attached file example 5

 Figure 10: Attached file example 6

- Ken Sajo
(Translated by Yukako Uchida)

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