Microsoft: Emotet Attack Shut Down an Entire Business Network

Microsoft has published a case report detailing its response to a massive Emotet attack that brought down an entire enterprise network, evading antivirus software and overheating all its Windows machines. The infection began when an employee opened a malicious attachment. 

The Microsoft Detection and Response Team (DART) reports an attacker sent "a swarm" of phishing emails to employees at Fabrikam, an alias it gave to the client company to protect its identity. One recipient opened a file attached to the email; as a result, their credentials were sent to the attackers' command-and-control server and granted the intruders machine access.

This access was what they needed to launch their broader plan, which was to spread Emotet throughout the network. Emotet, an automated malware, is used to collect data on businesses and individuals for theft and fraud through banking Trojans and other credential-theft tools. It's a polymorphic virus, meaning it updates itself with new definitions every few days, DART says. Attackers delivered updates from their C2 infrastructure to bypass firewalls and antivirus tools.

Four days after gaining credentials into Fabrikam, the attackers used the initial infected account to send phishing emails to other employees on the network. Many common email filters don't scan messages sent internally, and employees typically trust emails sent from an internal account. As a result, more employees clicked malicious attachments and downloaded malware.

"Working via admin accounts, it spread credential-stealing Trojans across employee accounts and used them to authenticate itself within the network," DART officials explain in their case study. "Fabrikam didn't have any network visibility tools in place, so for the next twenty-four hours Emotet wormed its way through its infrastructure without raising any red flags." 

By day eight, the organization's IT operations had shut down. Computers froze as their CPUs maxed out. The virus threatened all of its systems, including a network of 185 surveillance cameras. Its finance department couldn't complete external transactions; partner organizations couldn't access Fabrikam databases. The IT department, which couldn't tell whether they were facing an external attack or internal virus, scrambled to investigate but couldn't access network accounts: a distributed denial-of-service (DDoS) attack had flooded the network with traffic.

"Emotet consumed the network's bandwidth until using it for anything became practically impossible," DART reports. "Even emails couldn't wriggle through." 

Recognizing the problem was outside their control, Fabrikam called DART eight days after the initial phishing email. An official had been told the organization had an "extensive system to prevent cyberattacks," but the virus had evaded all their firewalls and antivirus software. One group of DART specialists went onsite with Fabrikam; other members began to help remotely.

Because the organization's existing systems didn't grant DART visibility into the attackers' operations, they deployed trial licenses of Defender Advanced Threat Protection, Azure Security Scan, Azure Advanced Threat Protection services, and other Microsoft malware detection tools. Specialists learned they needed to make architectural changes to halt the spread of Emotet and put administrative measures in place to contain and eliminate it. They implemented asset controls and created gaps between the assets with admin privileges across the environment.

"These buffer zones contained the virus enough to remove it with antivirus software," DART officials report. "With the architecture in place and detection tools deployed, DART uploaded antivirus signatures and eradicated the Emotet virus."

DART points to errors in Fabrikam's security best practices that contributed to the problem. Email filters did not flag internal emails, giving the attackers freedom to spread Emotet without raising any alerts. Network visibility tools could have detected the virus early on. Further, the spread may have been slowed, and high-value accounts protected, if the organization's administrative directories hadn't been left open.

While Microsoft did not specify the company affected in its case study, a report from ZDNet points out the details of this attack align with a cybersecurity incident affecting the city of Allentown, Pa., in February 2018. At the time of the attack, an AP report stated the Emotet infection affected government machines and began to self-replicate and steal credentials. The city reportedly paid Microsoft an initial $185,000 in emergency response fees to contain the virus, which was expected to cost an additional $800,000 to $900,000 in recovery costs.

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