A cross-platform assistant for creating malicious MS Office documents. Can hide VBA macros, stomp VBA code (via P-Code) and confuse macro analysis tools. Runs on Linux, OSX and Windows.
Current features
- Hide VBA macros from the GUI editor
- VBA stomping (P-code abuse)
- Fool analyst tools
- Serve VBA stomped templates via HTTP
- Set/Remove VBA Project Locked/Unviewable Protection
- MS Office Magic Show presentation at Derbycon 2018
- VBA stomping resources by the Walmart security team
- Pcodedmp by Dr. Bontchev
How effective is this?
At the time of writing, this tool is capable of getting a default Cobalt Strike macro to bypass all major antivirus products and most maldoc analysis tools (by using VBA stomping in combination with random module names).
Technology
Evil Clippy uses the OpenMCDF library to manipulate MS Office Compound File Binary Format (CFBF) files, and hereto abuses MS-OVBA specifications and features. It reuses code from Kavod.VBA.Compression to implement the compression algorithm that is used in dir and module streams (see MS-OVBA for relevant specifications).
Evil Clippy compiles perfectly fine with the Mono C# compiler and has been tested on Linux, OSX and Windows.
Compilation
A cross-platform compiled binary can be found under "releases".
OSX and Linux Make sure you have Mono installed. Then execute the following command from the command line:
mcs /reference:OpenMcdf.dll,System.IO.Compression.FileSystem.dll /out:EvilClippy.exe *.csNow run Evil Clippy from the command line:
mono EvilClippy.exe -hWindows Make sure you have Visual Studio installed. Then execute the following command from a Visual Studio developer command prompt:
csc /reference:OpenMcdf.dll,System.IO.Compression.FileSystem.dll /out:EvilClippy.exe *.csNow run Evil Clippy from the command line:
EvilClippy.exe -hUsage examples
Print help
EvilClippy.exe -hHide macros from GUI
Hide all macro modules (except the default "ThisDocument" module) from the VBA GUI editor. This is achieved by removing module lines from the project stream [MS-OVBA 2.3.1].
EvilClippy.exe -g macrofile.docStomp VBA (abuse P-code)
Put fake VBA code from text file fakecode.vba in all modules, while leaving P-code intact. This abuses an undocumented feature of module streams [MS-OVBA 2.3.4.3]. Note that the VBA project version must match the host program in order for the P-code to be executed (see next example for version matching).
EvilClippy.exe -s fakecode.vba macrofile.docNote: VBA Stomping does not work for files saved in the Excel 97-2003 Workbook (.xls) format
Set target Office version for VBA stomping
Same as the above, but now explicitly targeting Word 2016 on x86. This means that Word 2016 on x86 will execute the P-code, while other versions of Word wil execute the code from fakecode.vba instead. Achieved by setting the appropriate version bytes in the _VBA_PROJECT stream [MS-OVBA 2.3.4.1].
EvilClippy.exe -s fakecode.vba -t 2016x86 macrofile.docSet random module names (fool analyst tools)
Set random ASCII module names in the dir stream [MS-OVBA 2.3.4.2]. This abuses ambiguity in the MODULESTREAMNAME records [MS-OVBA 2.3.4.2.3.2.3] - most analyst tools use the ASCII module names specified here, while MS Office used the Unicode variant. By setting a random ASCII module name most P-code and VBA analysis tools crash, while the actual P-code and VBA still runs fine in Word and Excel.
EvilClippy.exe -r macrofile.docNote: this is known to be effective in tricking pcodedmp and VirusTotal
Serve a VBA stomped template via HTTP
Service macrofile.dot via HTTP port 8080 after performing VBA stomping. If this file is retrieved, it automatically matches the target's Office version (using its HTTP headers and then setting the _VBA_PROJECT bytes accordingly).
EvilClippy.exe -s fakecode.vba -w 8080 macrofile.dotNote: The file you are serving must be a template (.dot instead of .doc). You can set a template via a URL (.dot extension is not required!) from the developer toolbar in Word. Also, fakecode.vba must have a VB_Base attribute set for a macro from a template (this means that your facecode.vba must start with a line such as Attribute VB_Base = "0{00020906-0000-0000-C000-000000000046}").
Set/Remove VBA Project Locked/Unviewable Protection
To set the Locked/Unviewable attributes use the '-u' option:
EvilClippy.exe -u macrofile.docTo remove the Locked/Unviewable attributes use the '-uu' option:
EvilClippy.exe -uu macrofile.docNote: You can remove the Locked/Unviewable attributes on files that were not locked with EvilClippy as well.
Limitations
Developed for Microsoft Word and Excel document manipulation.
As noted above, VBA stomping is not effective against Excel 97-2003 Workbook (.xls) format.
Authors
Stan Hegt (@StanHacked) / Outflank
With significant contributions by Carrie Robberts (@OrOneEqualsOne / Walmart).
Special thanks to Nick Landers (@monoxgas / Silent Break Security) for pointing me towards OpenMCDF.