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# Office file analysis ## Introduction Microsoft has created **dozens of office document file formats**, many of which are popular for the distribution of phishing attacks and malware because of their ability to **include macros** (VBA scripts). Broadly speaking, there are two generations of Office file format: the **OLE formats** (file extensions like RTF, DOC, XLS, PPT), and the "**Office Open XML**" formats (file extensions that include DOCX, XLSX, PPTX). **Both** formats are structured, compound file binary formats that **enable Linked or Embedded content** (Objects). OOXML files are actually zip file containers, meaning that one of the easiest ways to check for hidden data is to simply `unzip` the document: ``` $ unzip example.docx Archive: example.docx inflating: [Content_Types].xml inflating: _rels/.rels inflating: word/_rels/document.xml.rels inflating: word/document.xml inflating: word/theme/theme1.xml extracting: docProps/thumbnail.jpeg inflating: word/comments.xml inflating: word/settings.xml inflating: word/fontTable.xml inflating: word/styles.xml inflating: word/stylesWithEffects.xml inflating: docProps/app.xml inflating: docProps/core.xml inflating: word/webSettings.xml inflating: word/numbering.xml $ tree . ├── [Content_Types].xml ├── _rels ├── docProps │ ├── app.xml │ ├── core.xml │ └── thumbnail.jpeg └── word ├── _rels │ └── document.xml.rels ├── comments.xml ├── document.xml ├── fontTable.xml ├── numbering.xml ├── settings.xml ├── styles.xml ├── stylesWithEffects.xml ├── theme │ └── theme1.xml └── webSettings.xml ``` As you can see, some of the structure is created by the file and folder hierarchy. The rest is specified inside the XML files. [_New Steganographic Techniques for the OOXML File Format_, 2011](http://download.springer.com/static/pdf/713/chp%3A10.1007%2F978-3-642-23300-5\_27.pdf?originUrl=http%3A%2F%2Flink.springer.com%2Fchapter%2F10.1007%2F978-3-642-23300-5\_27\&token2=exp=1497911340\~acl=%2Fstatic%2Fpdf%2F713%2Fchp%25253A10.1007%25252F978-3-642-23300-5\_27.pdf%3ForiginUrl%3Dhttp%253A%252F%252Flink.springer.com%252Fchapter%252F10.1007%252F978-3-642-23300-5\_27\*\~hmac=aca7e2655354b656ca7d699e8e68ceb19a95bcf64e1ac67354d8bca04146fd3d) details some ideas for data hiding techniques, but CTF challenge authors will always be coming up with new ones. Once again, a Python toolset exists for the examination and **analysis of OLE and OOXML documents**: [oletools](http://www.decalage.info/python/oletools). For OOXML documents in particular, [OfficeDissector](https://www.officedissector.com) is a very powerful analysis framework (and Python library). The latter includes a [quick guide to its usage](https://github.com/grierforensics/officedissector/blob/master/doc/html/\_sources/txt/ANALYZING\_OOXML.txt). Sometimes the challenge is not to find hidden static data, but to **analyze a VBA macro** to determine its behavior. This is a more realistic scenario, and one that analysts in the field perform every day. The aforementioned dissector tools can indicate whether a macro is present, and probably extract it for you. A typical VBA macro in an Office document, on Windows, will download a PowerShell script to %TEMP% and attempt to execute it, in which case you now have a PowerShell script analysis task too. But malicious VBA macros are rarely complicated, since VBA is [typically just used as a jumping-off platform to bootstrap code execution](https://www.lastline.com/labsblog/party-like-its-1999-comeback-of-vba-malware-downloaders-part-3/). In the case where you do need to understand a complicated VBA macro, or if the macro is obfuscated and has an unpacker routine, you don't need to own a license to Microsoft Office to debug this. You can use [Libre Office](http://libreoffice.org): [its interface](http://www.debugpoint.com/2014/09/debugging-libreoffice-macro-basic-using-breakpoint-and-watch/) will be familiar to anyone who has debugged a program; you can set breakpoints and create watch variables and capture values after they have been unpacked but before whatever payload behavior has executed. You can even start a macro of a specific document from a command line: ``` $ soffice path/to/test.docx macro://./standard.module1.mymacro ``` ## [oletools](https://github.com/decalage2/oletools) ```bash sudo pip3 install -U oletools olevba -c /path/to/document #Extract macros ``` ## Automatic Execution Macro functions like `AutoOpen`, `AutoExec` or `Document_Open` will be **automatically** **executed**. ## References * [https://trailofbits.github.io/ctf/forensics/](https://trailofbits.github.io/ctf/forensics/)

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