Factual-Rules-Generator : An Open Source Project Which Aims To Generate YARA Rules

Factual-rules-generator is an open source project which aims to generate YARA rules about installed software from a running operating system.

The goal of the software is to be able to use a set of rules against collected or acquired digital forensic evidences and find installed software in a timely fashion.

The software can be used to baseline known software from Windows system and create a set of rules for finding similar installation on other systems.

Dependencies

• pefile
• psutil
• ndjson
• python-tlsh
• PyInstaller (to change client.py to client.exe)
• ssdeep
  • On Ubuntu:
    • sudo apt-get install build-essential libffi-dev python3 python3-dev python3-pip libfuzzy-dev
    • pip install ssdeep

Tools requirement

Some tools are required on the host operating system some are Unix standard tools and some additional ones:

• xxd
• curl

For the Windows virtual machine, the following software is required to be installed:

• SDelete
• AsA (AttackSurfaceAnalyzer)

Install

• Install all Python dependencies defined requirements.txt
• Create a shared folder to communicate with VM
• Install a Windows VM
  • Install chocolatey on Windows VM
  • Complete bin/OnWindows/Varclient.py
  • Change bin/OnWindows/client.py in an executable file with PyInstaller and put in startup folder
• Update etc/allVariables.py to match your desired configuraiton

In test/ some examples of software to install is given, the following specific format is required:

• First, select the name of the packages to install using chocolatey before :, or the name of the file in case of msi or exe file.
• Second, after : there’s the name of the exe to extract and run it (without extension).
• The second part after , follow the same system with the word installer first and after : the type of installer :
  • choco
  • msiexec
  • exe
• Finally, the third part, uninstaller follow by : and the uninstaller like choco, msiexec or exe

Run and generate the rules

• bin/Generator.py is the only script to run, don’t forget to update etc/allVariables.py (critical step).

Public YARA rules repository

• factual-rules – Sample rules generated from some very common software.

Overview of factual rules generator