Information Gathering

Vba2Graph – Generate Call Graphs From VBA Code, For Easier Analysis Of Malicious Documents

November 21, 2018
2 Min Read
Vba2Graph - Generate Call Graphs From VBA Code, For Easier Analysis Of Malicious Documents

A tool for security researchers, who waste their time analyzing malicious Office macros.

Generates a VBA call graph, with potential malicious keywords highlighted.
Allows for quick analysis of malicous macros, and easy understanding of the execution flow.

Features

  • Keyword highlighting
  • VBA Properties support
  • External function declarion support
  • Tricky macros with “_Change” execution triggers
  • Fancy color schemes!

Pros

  • Pretty fast
  • Works well on most malicious macros observed in the wild

Cons

  • Static (dynamicaly resolved calls would not be recognized)

Examples
Example 1:
Trickbot downloader – utilizes object Resize event as initial trigger, followed by TextBox_Change triggers.

Example 2:

Check out the Examples folder for more cases.

Installation

Install oletools:

https://github.com/decalage2/oletools/wiki/Install

Install Python Requirements

pip2 install -r requirements.txt

Install Graphviz

Windows
Install Graphviz msi:

https://graphviz.gitlab.io/_pages/Download/Download_windows.html

Add “dot.exe” to PATH env variable or just:

set PATH=%PATH%;C:Program Files (x86)Graphviz2.38bin

Mac

brew install graphviz

Ubuntu

sudo apt-get install graphviz

Arch

sudo pacman -S graphviz

Usage

usage: vba2graph.py [-h] [-o OUTPUT] [-c {0,1,2,3}] (-i INPUT | -f FILE)
optional arguments:
-h, --help show this help message and exit
-o OUTPUT, --output OUTPUT
output folder (default: "output")
-c {0,1,2,3}, --colors {0,1,2,3}
color scheme number [0, 1, 2, 3] (default: 0 - B&W)
-i INPUT, --input INPUT
olevba generated file or .bas file
-f FILE, --file FILE Office file with macros

Usage Examples (All Platforms)
Only Python 2 is supported:

# Generate call graph directly from an Office file with macros [tnx @doomedraven]
python2 vba2graph.py -f malicious.doc -c 2
# Generate vba code using olevba then pipe it to vba2graph
olevba malicious.doc | python2 vba2graph.py -c 1

# Generate call graph from VBA code
python2 vba2graph.py -i vba_code.bas -o output_folder

Output
You’ll get 4 folders in your output folder:

  • png: the actual graph image you are looking for
  • svg: same graph image, just in vector graphics
  • dot: the dot file which was used to create the graph image
  • bas: the VBA functions code that was recognized by the script (for debugging)

Batch Processing

Mac/Linux:
batch.sh script file is attached for running olevba and vba2graph on an input folder of malicious docs.
Deletes output dir. use with caution.

 

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