mkYARA: Generating YARA rules based on binary code

by do son · September 11, 2019

mkYARA

Writing YARA rules based on executable code within malware can be a tedious task. An analyst cannot simply copy and paste the raw executable code into a YARA rule, because this code contains variable values, such as memory addresses and offsets. The analyst has to disassemble the code and wildcard all the pieces in the code that can change between samples. mkYARA aims to automate this part of writing rules by generating executable code signatures that wildcard all these little pieces of executable code that are not static.

Installation

pip install mkyara

Usage

usage: mkyara [-h] [-i {x86}] [-a {32,64,x86,x64}] -f FILE_PATH [-n RULENAME]

              -o OFFSET -s SIZE [-m {loose,normal,strict}] [-r RESULT] [-v]



Generate a Yara rule based on disassembled code



optional arguments:

  -h, --help            show this help message and exit

  -i {x86}, --instruction_set {x86}

                        Instruction set

  -a {32,64,x86,x64}, --instruction_mode {32,64,x86,x64}

                        Instruction mode

  -f FILE_PATH, --file_path FILE_PATH

                        Sample file path

  -n RULENAME, --rulename RULENAME

                        Generated rule name

  -o OFFSET, --offset OFFSET

                        File offset for signature

  -s SIZE, --size SIZE  Size of desired signature

  -m {loose,normal,strict}, --mode {loose,normal,strict}

                        Wildcard mode for yara rule generation

                        loose = wildcard all operands

                        normal = wildcard only displacement operands

                        strict = wildcard only jmp/call addresses

  -r RESULT, --result RESULT

                        Output file

  -v, --verbose         Increase verbosity

It comes with an IDA plugin to easily create YARA signatures by selecting a set of instructions and choosing one of the mkYARA -> Generate YARA rule options. Installation is as easy as installing the pip package and copying the mkyara_plugin.py to your IDA plugin directory.

Source: https://github.com/fox-it/

mkYARA: Generating YARA rules based on binary code

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