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Cyber Attackers Exploiting Microsoft Excel add-in Files

QakBot, a prominent form of trojan malware, often used as a precursor to ransomware attacks, is also abusing Excel to compromise victims.


Recently a unit of researchers delivered a detailed study on a new phishing campaign at HP Wolf Security. As per the report, threat actors are exploiting Microsoft Excel add-in files in order to send various forms of malware into the systems that could leave businesses vulnerable to data theft, ransomware, and other cybercrime. 

Researchers said that threat actors are excessively using malicious Microsoft Excel add-in (XLL) files to damage the systems and it has been observed that there was an almost six-fold (588%) increment in attacks using this technique during the final quarter of 2021 compared to the previous three months.

XLL add-in files are very famous among people because they provide users to execute a wide range of extra tools and functions in Microsoft Excel. But like macros, they're a tool that can be exploited by threat actors. 

According to the report, threat actors distributed malicious links via phishing emails related to payment references, quotes, invoices, shipping documents, and orders that come with malicious Excel documents with XLL add-in files. The recipient is then tricked into clicking a malicious link, which can lead to the installation and activate the add-in of malware, freezing of the system as part of a ransomware attack, or the revelation of sensitive information. 

Malware families that have been used in attacks leveraging XLL files include Dridex, BazaLoader, IcedID, Agent Tesla, Stealer, Raccoon Formbook, and Bitrat. Some of these forms of malware also create backdoors onto infected Windows systems, which gives attackers remote access to the system. 

Additionally, Some XLL Excel Dropper services are advertised as costing over $2,000, which is expensive for community malware but criminal forum users seem willing to pay the price. 

Alex Holland, senior malware analyst at HP Wolf Security said, "Abusing legitimate features in the software to hide from detection tools is a common tactic for attackers, as is using uncommon file types that may be allowed past email gateways. Security teams need to ensure they are not relying on detection alone and that they are keeping up with the latest threats and updating their defenses accordingly…” 

"…Attackers are continually innovating to find new techniques to evade detection, so it's vital that enterprises plan and adjust their defenses based on the threat landscape and the business needs of their users. Threat actors have invested in techniques such as email thread hijacking, making it harder than ever for users to tell friend from foe," he added.
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Microsoft Excel