Nim-Based Malware Loader Spreads Via Spear-Phishing Emails

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The TA800 threat group is distributing a malware loader, which researchers call NimzaLoader, via ongoing, highly-targeted spear-phishing emails.

While previous Twitter analysis identified this loader as a mere variant of TA800’s existing BazaLoader malware, new research cites evidence that NimzaLoader is a disparate strain — with its own separate string-decryption methods and hashing algorithm techniques.

The malware loader is unique in that it is written in the Nim programming language. The use of Nim is uncommon for malware in the threat landscape, except in rare cases, such as a Nim-based downloader recently seen being used by the Zebrocy threat group. Because of this, researchers say malware developers may be using Nim to avoid detection by defense teams who may not be familiar with the language.

“Malware developers may choose to use a rare programming language to avoid detection, as reverse engineers may not be familiar with Nim’s implementation, or focused on developing detection for it, and therefore tools and sandboxes may struggle to analyze samples of it,” said Dennis Schwarz and Matthew Mesa, researchers with Proofpoint on Wednesday, in a report shared with Threatpost before publication.
 
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