Original release date: October 6, 2020
This Alert uses the MITRE Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK®) framework. See the ATT&CK for Enterprise framework for all referenced threat actor techniques.
This product was written by the Cybersecurity and Infrastructure Security Agency (CISA) and the Multi-State Information Sharing & Analysis Center (MS-ISAC).
Emotet—a sophisticated Trojan commonly functioning as a downloader or dropper of other malware—resurged in July 2020, after a dormant period that began in February. Since August, CISA and MS-ISAC have seen a significant increase in malicious cyber actors targeting state and local governments with Emotet phishing emails. This increase has rendered Emotet one of the most prevalent ongoing threats.
To secure against Emotet, CISA and MS-ISAC recommend implementing the mitigation measures described in this Alert, which include applying protocols that block suspicious attachments, using antivirus software, and blocking suspicious IPs.
Emotet is an advanced Trojan primarily spread via phishing email attachments and links that, once clicked, launch the payload (Phishing: Spearphishing Attachment [T1566.001], Phishing: Spearphishing Link [T1566.002]).The malware then attempts to proliferate within a network by brute forcing user credentials and writing to shared drives (Brute Force: Password Guessing [T1110.001], Valid Accounts: Local Accounts [T1078.003], Remote Services: SMB/Windows Admin Shares [T1021.002]).
Emotet is difficult to combat because of its “worm-like” features that enable network-wide infections. Additionally, Emotet uses modular Dynamic Link Libraries to continuously evolve and update its capabilities.
Since July 2020, CISA has seen increased activity involving Emotet-associated indicators. During that time, CISA’s EINSTEIN Intrusion Detection System, which protects federal, civilian executive branch networks, has detected roughly 16,000 alerts related to Emotet activity. CISA observed Emotet being executed in phases during possible targeted campaigns. Emotet used compromised Word documents (.doc) attached to phishing emails as initial insertion vectors. Possible command and control network traffic involved
HTTP POST requests to Uniform Resource Identifiers consisting of nonsensical random length alphabetical directories to known Emotet-related domains or IPs with the following user agent string (Application Layer Protocol: Web Protocols [T1071.001]).
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/7.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; Media Center PC 6.0; .NET4.0C; .NET4.0E; InfoPath.3; .NET CLR
Traffic to known Emotet-related domains or IPs occurred most commonly over ports 80, 8080, and 443. In one instance, traffic from an Emotet-related IP attempted to connect to a suspected compromised site over port 445, possibly indicating the use of Server Message Block exploitation frameworks along with Emotet (Exploitation of Remote Services [T1210]). Figure 1 lays out Emotet’s use of enterprise techniques.
Figure 1: MITRE ATT&CK enterprise techniques used by Emotet
The following timeline identifies key Emotet activity observed in 2020.
partner01as the primary payload and
According to MITRE, Emotet uses the ATT&CK techniques listed in table 1.
Table 1: Common exploit tools
OS Credential Dumping: LSASS Memory [T1003.001]
Emotet has been observed dropping password grabber modules including Mimikatz.
Remote Services: SMB/Windows Admin Shares [T1021.002]
Emotet leverages the Admin$ share for lateral movement once the local admin password has been brute forced.
Obfuscated Files or Information [T1027]
Emotet has obfuscated macros within malicious documents to hide the URLs hosting the malware,
Obfuscated Files or Information: Software Packing [T1027.002]
Emotet has used custom packers to protect its payloads.
Network Sniffing [T1040]
Emotet has been observed to hook network APIs to monitor network traffic.
Exfiltration Over C2 Channel [T1041]
Emotet has been seen exfiltrating system information stored within cookies sent within a
Windows Management Instrumentation [T1047]
Emotet has used WMI to execute
Process Injection: Dynamic-link Library Injection [T1055.001]
Emotet has been observed injecting in to
Process Discovery [T1057]
Emotet has been observed enumerating local processes.
Command and Scripting Interpreter: PowerShell [T1059.001]
Emotet has used Powershell to retrieve the malicious payload and download additional resources like Mimikatz.
Command and Scripting Interpreter: Windows Command Shell [T1059.003]
Emotet has used
Command and Scripting Interpreter: Visual Basic [T1059.005]
Emotet has sent Microsoft Word documents with embedded macros that will invoke scripts to download additional payloads.
Valid Accounts: Local Accounts [T1078.003]
Emotet can brute force a local admin password, then use it to facilitate lateral movement.
Account Discovery: Email Account [T1087.003]
Emotet has been observed leveraging a module that can scrape email addresses from Outlook.
Brute Force: Password Guessing [T1110.001]
Emotet has been observed using a hard-coded list of passwords to brute force user accounts.
Email Collection: Local Email Collection [T1114.001]
Emotet has been observed leveraging a module that scrapes email data from Outlook.
User Execution: Malicious Link [T1204.001]
Emotet has relied upon users clicking on a malicious link delivered through spearphishing.
User Execution: Malicious File [T1204.002]
Emotet has relied upon users clicking on a malicious attachment delivered through spearphishing.
Exploitation of Remote Services [T1210]
Emotet has been seen exploiting SMB via a vulnerability exploit like ETERNALBLUE (MS17-010) to achieve lateral movement and propagation.
Create or Modify System Process: Windows Service [T1543.003]
Emotet has been observed creating new services to maintain persistence.
Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder [T1547.001]
Emotet has been observed adding the downloaded payload to the
Scheduled Task/Job: Scheduled Task [T1053.005]
Emotet has maintained persistence through a scheduled task.
Unsecured Credentials: Credentials In Files [T1552.001]
Emotet has been observed leveraging a module that retrieves passwords stored on a system for the current logged-on user.
Credentials from Password Stores: Credentials from Web Browsers [T1555.003]
Emotet has been observed dropping browser password grabber modules.
Archive Collected Data [T1560]
Emotet has been observed encrypting the data it collects before sending it to the C2 server.
Phishing: Spearphishing Attachment [T1566.001]
Emotet has been delivered by phishing emails containing attachments.
Phishing: Spearphishing Link [T1566.002]
Emotet has been delivered by phishing emails containing links.
Non-Standard Port [T1571]
Emotet has used HTTP over ports such as 20, 22, 7080, and 50000, in addition to using ports commonly associated with HTTP/Hypertext Transfer Protocol Secure.
Encrypted Channel: Asymmetric Cryptography [T1573.002]
Emotet is known to use RSA keys for encrypting C2 traffic.
MS-ISAC developed the following Snort signature for use in detecting network activity associated with Emotet activity.
alert tcp $HOME_NET any -> $EXTERNAL_NET 443 (msg:"[CIS] Emotet C2 Traffic Using Form Data to Send Passwords"; content:"POST"; http_method; content:"Content-Type|3a 20|multipart/form-data|3b 20|boundary="; http_header; fast_pattern; content:"Content-Disposition|3a 20|form-data|3b 20|name=|22|"; http_client_body; content:!"------WebKitFormBoundary"; http_client_body; content:!"Cookie|3a|"; pcre:"/:?(chrome|firefox|safari|opera|ie|edge) passwords/i"; reference:url,cofense.com/flash-bulletin-emotet-epoch-1-changes-c2-communication/; sid:1; rev:2;)
CISA developed the following Snort signatures for use in detecting network activity associated with Emotet activity. Note: Uniform Resource Identifiers should contain a random length alphabetical multiple directory string, and activity will likely be over ports 80, 8080, or 443.
alert tcp any any -> any $HTTP_PORTS (msg:"EMOTET:HTTP URI GET contains '/wp-content/###/'"; sid:00000000; rev:1; flow:established,to_server; content:"/wp-content/"; http_uri; content:"/"; http_uri; distance:0; within:4; content:"GET"; nocase; http_method; urilen:<17; classtype:http-uri; content:"Connection|3a 20|Keep-Alive|0d 0a|"; http_header; metadata:service http;)
alert tcp any any -> any $HTTP_PORTS (msg:"EMOTET:HTTP URI GET contains '/wp-admin/###/'"; sid:00000000; rev:1; flow:established,to_server; content:"/wp-admin/"; http_uri; content:"/"; http_uri; distance:0; within:4; content:"GET"; nocase; http_method; urilen:<15; content:"Connection|3a 20|Keep-Alive|0d 0a|"; http_header; classtype:http-uri; metadata:service http;)
CISA and MS-ISAC recommend that network defenders—in federal, state, local, tribal, territorial governments, and the private sector—consider applying the following best practices to strengthen the security posture of their organization’s systems. System owners and administrators should review any configuration changes prior to implementation to avoid unwanted impacts.
For additional information on malware incident prevention and handling, see the National Institute of Standards and Technology Special Publication 800-83, Guide to Malware Incident Prevention and Handling for Desktops and Laptops.