Emotet was the most prolific malware botnet of 2018 and 2019, but the botnet fell silent on February 7, 2020 but it has now sprung back to life and is being used to distribute Trojan malware. The botnet returned with a malicious spam campaign on July 17 of at least 30,000 emails, mostly targeting organizations in the United States and United Kingdom. The scale of the campaign has now grown to around 250,000 emails a day with the campaign now global.
The Emotet botnet is a network of computers infected with Emotet malware and there are estimated to be around half a million infected Windows computers under the control of the botnet operators. Those infected devices are contacted through the attackers’ command and control (C2) servers and are sent instructions to send out spam emails spreading Emotet malware.
Once the malware is downloaded, the infected computer is added to the botnet and is used to send spam emails. Emotet infections can also spread laterally within an organization. When investigations are launched following the detection of Emotet, it is common for other computers to be discovered to be infected with the malware.
What makes Emotet particularly dangerous is the operators of the botnet pair up with other threat groups and deliver other malware variants. Emotet has been used to distribute a range of malware variants since its creation in 2014, but recently the malware payload of choice was the TrickBot Trojan. TrickBot is a banking trojan cum information stealer that also serves as a malware downloader. In addition to stealing sensitive data, the operators of TrickBot pair up with other malware developers, notably the developers of Ryuk ransomware. Once TrickBot has stolen information, the baton is passed over to Ryuk, which will also steal data before encrypting files on network. The new Emotet campaign started by distributing the TrickBot Trojan, although the payload has since switched to the QakBot banking Trojan. QakBot also delivers ransomware as a secondary payload, with Prolock often used in the past.
Emotet emails use a variety of lures to get recipients to click links to malicious websites or open infected email attachments. Emotet targets businesses, so the lures used are business related, such as fake shipping notices, invoices, purchase orders, receipts, and job applications. The emails are often personalized, and the threat actors known to hijack email threads and send responses with malicious documents added.
An Emotet infection is serious and should be treated with the same urgency as a ransomware attack. Prompt action may allow Emotet to be removed before a secondary payload is delivered.
Fortunately, Emotet malware is delivered via email so that gives businesses an opportunity to prevent infections. By deploying an advanced spam filter such as SpamTitan that has sandboxing to subject email attachments to deep analysis, these malicious emails can be identified and quarantined. Coupled with other email security measures such as end user training, businesses can mount a robust defense and block infections.
The return of Emotet was inevitable, and while the resumption of activity is bad news, there is some good news. A vigilante hacker has started sabotaging Emotet operations by targeting a weak link in their infrastructure. Emotet malware is downloaded from the internet from a range of hacked WordPress sites. The vigilante has found that the temporary stores of Emotet can be easily hacked as they tend to all use the same password. After guessing that password, the Emotet payload has been replaced with a variety of animated GIFs and has disrupted operations, reducing infections to around a quarter of their normal levels. That said, the Emotet gang is attempting to regain control of its web shells and infections with Emotet are still growing.