Emotet, a nasty botnet and popular malware family, has proven increasingly dangerous over the past year as its operators adopt new tactics. Now armed with the ability to drop additional payloads and arriving via business email compromise (BEC), it's become a major threat to organizations.
Security watchers are wary of Emotet, which was among the first botnets to spread banking Trojans laterally within target organizations, making removal difficult. Emotet first appeared in 2014 as a Trojan designed to snatch banking credentials and other sensitive data. The threat was frequently spread via phishing emails packed with malicious documents or links.
Over time, Emotet's operators - a group called Mealybug - have evolved its business model and the shape of their attack from a banking Trojan to a means of delivering other groups' threats. In 2018, Webroot dubbed Emotet the year's worst botnet seen distributing banking Trojans.
"Its information stealing payloads are delivered at an impressive pace, suggesting threat actors have automated multiple steps in their campaign operations," Webroot researchers write in a blog post on their rankings of 2018's worst threats. The changes to Emotet, while gradual at first, quickly ramped up in recent years as attackers switched to even more nefarious tactics.
After a quiet period in 2015, Emotet detections spiked in the second half of 2017, Symantec reported. Mealybug's victims expanded that year to include targets in Canada, China, Mexico, and the UK. Toward the end of 2017, the Cylance Threat Research Team analyzed a malicious Microsoft Word file with a malicious macro program created to download Emotet malware.
Taking on New Threats
In 2018, Mealybug ramped up its activity to the point where it was selling malware to other actors, says Sig Murphy, managing director of incident response and forensics at Cylance. Emotet was combined with Trickbot and Qakbot, a tactic Symantec also had detected in Feb. 2018. The blend of Emotet with other strains of ransomware made the threat more dangerous.
"The combination there is really hard to defend against properly because the loader is polymorphic," says Murphy. "It changes every time it infects a computer."
US-CERT issued an alert for Emotet in July 2018, calling it an advanced modular banking Trojan that mainly functions as a downloader or dropper of other banking Trojans. Emotet is "the most costly and destructive malware affecting state, local, tribal, and territorial (SLTT) governments, and the private and public sectors," it says, costing governments up to $1M per incident.
This hybrid threat model "is a unique challenge" to organizations, Murphy says, and catches many off guard. Emotet alone used to drop its own Emotet-branded malware. Later in the year, it was used to deliver new types of threats. Before, it would collect email credentials and use them to spread laterally. It later became interested in the content of targeted emails, he adds.
"It's pretty clear they're trying to pivot into [the] BEC attack model, which is different from what they've done in the past," says Murphy of the Mealybug threat group's evolving strategies. In August 2018, Trend Micro pick up on Spoofed banking emails arriving with Emotet malware. For example, spam emails contain payment notifications from spoofed bank email addresses. The email's body has a link to download a .doc file, which contains macros that, when run, activate a PowerShell command that downloads and runs the Emotet malware, researchers explain.
After ramping up in early 2018, Murphy says Emotet increased again during the holiday season. Through the start of 2019, the malware continued to spread, and new enterprise clients were asking Cylance for help after getting infected, he says. Its growth signifies greater maturity among the Mealybug actors as they learn what's effective.
"They seem much more organized than a lot of other groups," Murphy explains. "The shift [to BEC] says they're continuing to be more organized … they know what's working and what's not." New ransomware variants like Qakbot provide a new source of income, he adds.
Thinking Ahead of the Attackers
It's hard to tell what Mealybug will do next. One route they could take, says Murphy, is attempt to make their attacks quieter. While he has no indication they might do this, he points out how Emotet in its current form is "very noisy" in its spread. If they could change the threat so it spreads without taking down systems, it would be harder to know a business is at risk.