Dissecting Malicious Office Documents with Linux
A few months ago, Rob wrote a nice diary[1] to explain how to dissect a (malicious) Office document (.docx). The approach was to use the OpenXML SDK[2] with Powershell. This is nice but how to achieve the same on a Linux system? One of our readers (thanks Mike!) provided us with the steps to perform the same kind of analysis but on a Kali instance (replace Kali with your preferred distribution).
The idea remains the same: To use Powershell and the SDK. Yes, if you don’t know yet, the integration between the Linux and Windows worlds is becoming very deep. If it’s possible to run bash on Windows, it’s also possible to run Powershell on a Linux box[3]! Here are the steps to install the required software components.
Install Powershell:
# apt update && apt -y install curl gnupg apt-transport-https # curl https://packages.microsoft.com/keys/microsoft.asc | apt-key add - # echo "deb [arch=amd64] https://packages.microsoft.com/repos/microsoft-debian-stretch-prod stretch main" > /etc/apt/sources.list.d/powershell.list # apt-get update # apt-get install powershell
Install Mono (Mono is an open source implementation of Microsoft's .NET Framework[4])
# apt-get install mono-complete # curl -o /usr/local/bin/nuget.exe https://dist.nuget.org/win-x86-commandline/latest/nuget.exe
Install the OpenXML SDK:
# mkdir /opt/MSPackages # cd /opt/MSPackages # mono /usr/local/bin/nuget.exe install DocumentFormat.OpenXml -Version 2.8.1
Now you are able to follow the same analysis path as described by Rob in his diary. Here is an example:
# file 14266eed4ebd3d4653c27f150e5717a763f13365525966186cfd7b390d21685f.docx 14266eed4ebd3d4653c27f150e5717a763f13365525966186cfd7b390d21685f.docx: Microsoft Word 2007+ # pwsh PowerShell 6.1.0 Copyright (c) Microsoft Corporation. All rights reserved. https://aka.ms/pscore6-docs Type 'help' to get help. PS /tmp> [System.Reflection.Assembly]::LoadFrom("/opt/MSPackages/DocumentFormat.OpenXml.2.8.1/lib/net35/DocumentFormat.OpenXml.dll") GAC Version Location --- ------- -------- False v2.0.50727 /opt/MSPackages/DocumentFormat.OpenXml.2.8.1/lib/net35/DocumentFormat.OpenXml.dll PS /tmp> $file='14266eed4ebd3d4653c27f150e5717a763f13365525966186cfd7b390d21685f.docx' PS /tmp> $doc = [DocumentFormat.OpenXml.Packaging.WordprocessingDocument]::Open($file,$true) PS /tmp> $doc.MainDocumentPart.Document | grep InnerText | grep http InnerText : HYPERLINK "hxxps://bozeqb[.]com/redirect.php"READ FULL CODE OF CONDUCT AND SIGN HERE PS /tmp> $doc.Close()
An easy way to safely extract malicious URLs. Happy document analysis!
[1] https://isc.sans.edu/forums/diary/Dissecting+Malicious+MS+Office+Docs/24108/
[2] https://docs.microsoft.com/en-us/office/open-xml/open-xml-sdk
[3] https://docs.microsoft.com/en-us/powershell/scripting/setup/installing-powershell-core-on-linux?view=powershell-6
[4] https://www.mono-project.com/
Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key
Comments
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Nov 17th 2022
6 months ago
EEW
Nov 17th 2022
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Nov 17th 2022
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Nov 17th 2022
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Nov 23rd 2022
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Dec 3rd 2022
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Dec 3rd 2022
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<a hreaf="https://technolytical.com/">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission
isc.sans.edu
Dec 26th 2022
5 months ago
isc.sans.edu
Dec 26th 2022
5 months ago