Many malware infections start with a malicious email that contains a file attachment with a malicious script that downloads malware if executed. One response to a single email is all it takes to infect the user’s device with malware, which may be able to spread across the network or at least provide the threat actor with the foothold they need in the network for follow-on activities. There is a much worse scenario, however. Rather than a single user infecting the network with one malware variant, that single response to the malicious email results in multiple malware infections. One campaign has been identified that does just that. A malware cluster bomb is delivered that can infect the user’s device with up to 10 different malware variants.

The campaign was identified by researchers at KrakenLabs and has been attributed to a threat actor known as Unfurling Hemlock. The campaign is being conducted globally with at least 10 countries known to have been attacked, although most of the victims have so far been located in the United States. The campaign has been running since at least February 2024 and uses two methods to deliver the malware variants – malicious emails and malware loaders installed by other threat groups. The threat actor has already distributed hundreds of thousands of malicious files in the 5 months since the operation is believed to have commenced.

In the email campaign conducted by Unfurling Hemlock, the victim is tricked into downloading a file called WExtract.exe which contains nested cabinet files, each containing a different malware variant. If the file is executed, the malware is extracted in sequence, and each malware variant is executed in reverse order, starting with the last malware variant to be extracted. Each malware cluster bomb has between four and seven stages, with some of those stages delivering multiple malware variants.

The malware variants delivered vary but they consist of information stealers, backdoors, malware loaders, and botnets. Information stealers include Redline Stealer, Mystic Stealer, and RisePro, and malware loaders including Amadey and SmokeLoader. Other malware variants are used to disable security solutions such as Windows Defender, help with obfuscation and hiding malware payloads, gathering system information, and reporting on the status of the malware infections.

It is not clear how the threat actor is using these malware infections. They could be delivering malware for other threat actors and selling the access, using the malware to harvest credentials to sell on the darkweb, conducting their own attacks using whatever malware variant serves their purpose, or a combination of the three. What the attack does ensure is maximum flexibility, as there are high levels of redundancy to ensure that if some of the malware variants are detected, some are likely to remain.

The delivery of multiple malware variants means this campaign could be highly damaging, but it also increases the chance of detection. While antivirus software is a must and may detect some of the malware variants, others are likely to go undetected. The key to blocking attacks is to prevent the initial phishing emails from reaching end users and to provide training to the workforce to help with the identification and avoidance of these malicious emails.

Many email security solutions rely on antivirus engines to detect malware but cybercriminals are skilled at bypassing these signature-based defenses. TitanHQ’s SpamTitan anti-spam software, SpamTitan, uses dual antivirus engines as part of the initial checks but also email sandboxing for behavioral analysis. Suspicious emails are sent to the sandbox where files are unpacked and their behavior is analyzed in depth. The behavioral analysis identifies malicious actions, resulting in the messages being quarantined for further analysis by the security team. SpamTitan also includes AI and machine-learning algorithms to check how messages deviate from the emails typically received and can identify new threats that have previously not been seen. SpamTitan is a highly effective Microsoft 365 spam filter and can be provided as a gateway spam filter or a cloud-based anti-spam service.

End user training is an important extra layer of security that helps eradicate bad security practices and teaches employees how to recognize and avoid malicious emails. Should a malicious bypass email security defenses, trained employees will be more likely to recognize and report the threat to the security team. Training data from SafeTitan, TitanHQ’s security awareness training platform and phishing simulator, shows the training and phishing simulations can reduce susceptibility to email attacks by up to 80% when provided regularly throughout the year.

Give the TitanHQ sales team a call today for more information on these and other cybersecurity solutions to improve your defenses against the full range of cyber threats.