The RIG exploit kit is distributing a new variant of the Purple Fox downloader malware family that’s capable of abusing PowerShell.

Trend Micro observed that the infection chain for this new Purple Fox variant began when a user visited a malicious site hosting the RIG exploit kit. At that point, the malicious software package used one of three methods to redirect users to a malicious PowerShell command:

  • A Flash (.swf) file that exploited CVE-2018-15982;
  • Two .htm files that exploited CVE-2014-6332 and CVE-2018-8174; or
  • An .hta file.

The PowerShell script, which masqueraded as an image file, then abused the API of msi.dll to execute the main component for Purple Fox.

As 360 Total Security noted, Purple Fox is a downloader Trojan that has affected tens of thousands of users leading up to its initial detection. The newer variant spotted by Trend Micro retained a rootkit component that abused publicly available code. However, the sample differed in that it used PowerShell, thereby enabling fileless attacks in its efforts to deliver cryptomining threats and other malware.

Malware Authors’ Growing Preference for PowerShell

Threat actors have shown a penchant for abusing PowerShell in their attack campaigns this year. Back in late August, Trend Micro spotted a variant of the Asruex backdoor that infected a system via a shortcut file that contained a PowerShell download script. Just a few days later, SecureWorks analyzed a toolkit employed by the LYCEUM threat group in a new Middle East campaign. This assortment of malicious utilities included a PowerShell-based keylogger and a PowerShell script for collecting account information from an infected system.

How to Defend Against RIG Exploit Kit Attacks

Security professionals can help their organizations defend against attacks initiated by the RIG exploit kit by investing in a comprehensive vulnerability management solution that integrates with other security solutions, including security information and event management (SIEM), patch management systems and network modeling tools. Additionally, companies should make sure they monitor for attacks abusing PowerShell by actively searching for malicious PowerShell commands and turning on transcription logs.

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