Word and Excel Files Infected Using Windows PowerShell

March 27, 2014 – 7:36 PM

Malware targeting Word and Excel files has been around for some time, but we recently encountered a new malware family, CRIGENT (also known as “Power Worm”) which brings several new techniques to the table. (We detect these files as W97M_CRIGENT.JER and X97M_CRIGENT.A.)

Most significantly, instead of creating or including executable code, CRIGENT uses the Windows PowerShell to carry out its routines. PowerShell is a powerful interactive shell/scripting tool that is available for all current versions of Windows (and is built-in from Windows 7 onwards); this malware carries out all its behavior via PowerShell scripts. IT administrators that are normally on the lookout for malicious binaries may overlook this, as malware using this technique is not particularly common.

Arrival and Additional Components

This particular threat arrives as an infected Word or Excel document, which may be dropped by other malware or downloaded/accessed by users. When opened, right away it downloads two additional components from two well-known online anonymity projects:  the Tor network, and Polipo, a personal web cache/proxy.

The attacker disguised both what these files were (by changing their file name), and where they are hosted by hiding this information in DNS records. Copies of these files are stored using legitimate cloud file hosts (in this case, Dropbox and OneDrive). The URLs of these files were hidden in DNS records. How was this done?


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