ViperMonkey is a VBA Emulation engine written in Python, designed to analyze and deobfuscate malicious VBA Macros contained in Microsoft Office files (Word, Excel, PowerPoint, Publisher, etc).
See my article "Using VBA Emulation to Analyze Obfuscated Macros", for real-life examples of malware deobfucation with ViperMonkey.
- ViperMonkey is an experimental VBA Engine targeted at analyzing maldocs. It works on some but not all maldocs.
- VBA parsing and emulation is extremely slow for now (see the speedup section for how to improve the speed).
- VBA Emulation is hard and complex, because of all the features of the VBA language, of Microsoft Office applications, and all the DLLs and ActiveX objects that can be called from VBA.
- This open-source project is only developed on my scarce spare time, so do not expect miracles. Any help from you will be very appreciated!
ViperMonkey requires the most recent version of
oletools, at least v0.52.3. Make sure to either install the most recent oletools
version by running
pip install -U oletools, or make sure
the most recent oletools install directory appears in PYTHONPATH, or
install the most recent development version of oletools using pip as described
The parsing library used by default in ViperMonkey can take a long time to parse some samples. ViperMonkey can be sped up considerably (~5 times faster) by running ViperMonkey using pypy rather than the regular Python interpreter. To use pypy do the following:
- Install pypy following the instructions here.
- Install the following Python packages. This can be done by downloading the .tar.gz for each package and running 'sudo pypy setup.py install' (note the use of pypy rather than python) for each package.
Stripping Useless Statements
The "-s" ViperMonkey command line option tells VipeMonkey to strip out useless statements from the Visual Basic macro code prior to parsing and emulation. For some maldocs this can significantly speed up analysis.
Emulating File Writes
ViperMonkey emulates some file writing behavior. The SHA256 hash of dropped files is reported in the ViperMonkey analysis results and the actual dropped files are saved in the directory MALDOC_artifacts/, where MALDOC is the name of the analyzed maldoc file.
Emulating Specific VBA Functions
By default ViperMonkey emulates maldoc behavior starting from standard macro auto run function (like AutoOpen, Document_Open, Document_Close, etc.). In some cases you may want to emulate the behavior starting from a non-standard auto run function. This is supported via the -i command line option. To emulate maldoc behavior starting from function Foo, use the command line option '-i Foo'. To emulate behavior starting from multiple non-standard entry points, use the command line option '-i "Foo,Bar,Baz"' (note that the entry point function names are comma seperated and must appear in a double quoted string).
- 2018-03-22 v0.06: new features and bug fixes contributed by Kirk Sayre
- Added support for parsing some technically invalid VBA statements.
- Additional parsing fixes.
- Added support for starting emulation at non-standard functions.
- Added support for Environ, IIf, Base64DecodeString, CLng, Close, Put, Run, InStrRev, LCase, RTrim, LTrim, AscW, AscB, and CurDir functions.
- Added emulation support for saving dropped files.
- Added support for For Each loops.
- Added support for While Wend loops.
- Handle 'Exit Do' instructions.
- 2018-01-12 v0.05: a lot of new features and bug fixes contributed by Kirk Sayre
- Added support for Select and Do loops.
- Added support for 'End Sub' and 0 argument return statements.
- Added support for #if constructs.
- Each VBA stream is now parsed in a separate thread (up to the # of machine cores).
- Added parsing for private type declarations.
- Report calls to CreateProcessA in final report.
- Handle Application.Run() of locally defined methods.
- Added VBA functions Abs, Fix, Hex, String, CByte, Atn, Dir, RGB, Log, Cos, Exp, Sin, Str, and Val.
- Added support for 'Exit Function' operator.
- Changed math operators to also work with string representations of integers.
- Added a configurable iteration limit on loops.
- Added support for InStr, Replace, Sgn, Sqr, UBound, LBound, Trim, StrConv, Split, StrReverse, and Int VB functions.
- Added support for string character subscripting.
- Added support for negative integer literals.
- Added support for if-then-else statements.
- Added support for Const and initial values for global variable declarations.
- Handle assignments of boolean expressions to variables.
- Added support for Left(), Right(), Array(), and BuiltInDocumentProperties() functions.
- Added support for global variables.
- Fixed some parse errors.
- Added analysis of AutoClose() functions.
- 2016-09-26 v0.02: First published version
- 2015-02-28 v0.01: First development version
- see changelog in source code for more info.
Download and Install:
For now, there is no package on PyPI for automated installation. It must be done manually:
- Download the archive from the repository: https://github.com/decalage2/ViperMonkey/archive/master.zip
- Extract it in the folder of your choice
- Install dependencies by running
sudo -H pip install -U -r requirements.txton Linux/Mac or
pip install -U -r requirements.txton Windows
To parse and interpret VBA macros from a document, use the vmonkey script:
python vmonkey.py <file>
To make analysis faster (see the Speedup section), do:
pypy vmonkey.py -s <file>
If the output is too verbose and too slow, you may reduce the logging level using the -l option:
python vmonkey.py -l warning <file>
Winter is coming.
How to Suggest Improvements, Report Issues or Contribute:
This is a personal open-source project, developed on my spare time. Any contribution, suggestion, feedback or bug report is welcome.
To suggest improvements, report a bug or any issue, please use the issue reporting page, providing all the information and files to reproduce the problem.
You may also contact the author directly to provide feedback.
The code is available in a GitHub repository. You may use it to submit enhancements using forks and pull requests.
This license applies to the ViperMonkey package, apart from the thirdparty folder which contains third-party files published with their own license.
The ViperMonkey package is copyright (c) 2015-2018 Philippe Lagadec (http://www.decalage.info)
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
- Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
- Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.