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Weaponized Word Document Targets macOS, Windows

A recently uncovered malware campaign was found to be using a weaponized Word document that can be used to target both macOS and Windows machines, Fortinet researchers warn.

A recently uncovered malware campaign was found to be using a weaponized Word document that can be used to target both macOS and Windows machines, Fortinet researchers warn.

The campaign relies on a macro-enabled Word file designed to execute a malicious VBA (Visual Basic for Applications) code. Up to a certain point, the code execution follows the same steps, but then it takes a different path, depending on whether it runs on macOS or Windows.

Similar to a typical macro attack, as soon as the user opens the malicious document, they are prompted to enable macros, which automatically causes the VBA code to be executed (the VBA uses slightly modified code taken from a Metasploit framework).

The code calls the AutoOpen() function, which reads Base64-encoded data from the “Comments” property of the file. Moving forth, the execution route differs depending on whether the victim runs macOS or Windows, Fortinet says.  

On macOS, because Python is pre-installed and Python scripts can be executed by default, the malicious attack takes this route. Thus, the base64-decoded script is executed to download another Python script, which researchers discovered to be a slightly modified version of the Python meterpreter file, which is also part of the Metasploit framework.

Once this script is executed, it attempts to connect to a remote domain on port 443, but Fortinet says that the server wasn’t answering client requests during analysis. However, security researchers observed that the Python process remains active on the system while trying to connect to the reachable server.

On Windows systems, the VBA script makes a DOS-style command string starting with cmd.exe, then starts powershell.exe hidden, and executes the base64-encoded code. The PowerShell script was designed to decompress a piece of gzip data to get another PowerShell script and execute it.

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The malicious script would ultimately download a file into a newly allocated buffer, with this file found to be a 64-bit DLL file. The file is executed when the thread function is returned. The malware was also observed establishing communication with the server, but Fortinet didn’t offer further info on its capabilities.

Both the macOS and Windows malicious programs were observed trying to communicate with subdomains of vvlxpress[.]com.

Although macro malware has been hitting Windows users for a very long time, this is only the second attack to date to abuse malicious macros in an attempt to compromise Macs, after another was detailed in early February. However, this is the first time the same macro-enabled Word document has been used to target both macOS and Windows users.

Related: Office Loader Uses Macros to Drop Array of Malware

Related: Macro Malware Makes Improvements on Hiding Malicious Code

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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