ptr_bouncer

#!/bin/bash

##############################
#     System variables       #
##############################

listURL="https://github.com/3CORESec/PTRB/raw/master/ptrb-domains.txt"
outputFile="output.txt"

##############################
#       Help screen          #
##############################

print_help() {
  echo -e "\nHere's a few examples on how to run ptr_bouncer:\n\n\
Example with community domain list:                ./ptr_bouncer your_ip_list.txt\n\
Example with custom domain list:                   ./ptr_bouncer your_ip_list.txt your_custom_domain_list.txt\n\
Example with no stdout and only output to file:    ./ptr_bouncer your_ip_list.txt > /dev/null 2>&1\n\n\
All IPs that do not hold a PTR record or the PTR record does not match the domain list, will be placed in output.txt.\n"
}

for arg in "$@"
do
  if [ "$arg" == "-h" ]
  then
    print_help
    exit 0
  fi
done

if [[ $# -eq 0 ]] ; then
  print_help
  exit 0
fi

########################################
#    Custom or default domain list?    #
########################################

if [[ -z "$2" ]] ; then
  echo -e "\nNo external domain list specified. Downloading and using community list."
  # Check which application to use for download of community list
  if ! command -v curl &> /dev/null
  then
    if ! command -v wget &> /dev/null
    then
      echo "curl or wget not found. Exiting."
      exit 1
    else
      wget --quiet $listURL -o ptrb-domains.txt
    fi
  else
    curl -sSL $listURL -o ptrb-domains.txt
  fi
  LIST="ptrb-domains.txt"
else
  LIST=$2
fi

# Clean output file from previous run
> $outputFile

########################################
#         Verification process         #
########################################

echo ""

while read ip; do
  PTR=$(host $ip | rev | cut -d" " -f1 | awk 'BEGIN {FS="."}{ print $2"."$3}' | rev)
  if [ "$PTR" == "." ]; then
    echo "IP $ip does not have a PTR record. IP added to output list."
    echo $ip >> $outputFile
  elif grep -q "$PTR" $LIST; then
    echo "IP $ip holds a PTR of $PTR, which is whitelisted. It will not be included in the output list."
  else
    echo "IP $ip has a PTR of $PTR and it is not whitelisted. IP added to output list."
    echo $ip >> $outputFile
  fi
done <$1

echo ""

exit 0