Description

A malicious campaign emerged on June 21, 2024, distributing a JavaScript file hosted on grupotefex[.]com, which executes an MSI installer and subsequently drops a Brute Ratel Badger DLL into the user’s AppData. The Brute Ratel command-and-control framework then downloaded and inserted the stealthy Latrodectus backdoor, enabling threat actors to gain remote control, steal data, and deploy additional payloads. Zscaler ThreatLabz confirmed Brute Ratel's involvement as an initial access broker for the Latrodectus malware family on June 23. The attack leveraged Bing search results to redirect users from a lookalike domain (appointopia[.]com) to a fake IRS website (hxxps[:]//grupotefex[.]com/forms-pubs/about-form-w-2/). Clicking on the site triggered a CAPTCHA challenge, which, when solved, downloaded a malicious JavaScript file (Form_Ver-*[.]js) from a Google Firebase storage bucket. Analysis of the file Form_ver-14-00-21[.]js revealed malicious code obfuscated within comments, using a ScriptHandler class to extract and execute the code via new Function(). This technique effectively hides the malicious payloads and evades antivirus detection. The sole purpose of the Form_ver-14-00-21[.]js script was to download and execute MSI packages from specified URLs, retrieving BST.msi from the IP address 85[.]208[.]108[.]63 and initiating its installation. A similar incident on June 25 involved a different script downloading neuro[.]msi from a related IP, 85[.]208[.]108[.]30, indicating a targeted campaign. Rapid7’s analysis of neuro.msi found a cabinet archive (disk1.cab) containing a DLL named capisp[.]dll, which was dropped into the user’s AppData/Roaming folder and executed using rundll32[.]exe. The capisp[.]dll revealed a multi-stage malware infection chain, with the decrypted data acting as a loader for a packed Brute Ratel Badger payload, which connected to multiple C2 domains and downloaded the Latrodectus malware, injected into Explorer[.]exe and communicating with additional C2 URLs.