College of Charleston Cybersecurity Club

Bash and Python Scripting

August 2, 2021

Bash and Python Scripting

Bourne Again Shell (Bash)

The Basics

  • Shabang: #!/bin/bash
  • How to run bash scripts:
  • Make sure the file is executable:
    • ls -alth and check for an x flag
  • If it isn’t executable:
    • chmod +x <filename.sh>
    • chmod 777 <filename.sh>
  • bash <filename.sh>
  • ./<filename.sh>

Variables

Conventions:

  • UPPERCASE= value/string/output from a command
  • Example: NAME=“Your Name”
  • Variabe usage:
echo “My name is $NAME”
echo “My name is ${NAME}, hello”

Reading User Input:

# !/bin/bash
#Read user data
echo "Please enter your full name: "
read FIRSTNAME LASTNAME	
echo "Your name is $FIRSTNAME $LASTNAME"

Positional Parameters:

#!/bin/bash
#positional parameters
echo "Execution of script $0"
echo "Enter the name of the user: $1"
#add user
adduser --home /$1 $1

#!/bin/bash
#menus
echo "Welcome to Bob's Burgers"
echo "Please choose what you want to eat: "
meals="Burger Fries"
select option in $meals; do
	echo "The selected option is $REPLY"
	echo "The selected meal is $option"
done

Conditionals:

#!/bin/bash
#if/if-else
NAME="Patrick"
if [ "$NAME" = "Patrick" ];
then
	echo "Welcome $NAME"
fi
echo "Enter username: "
read USERNAME
if [ "$USERNAME" = "Patrick" ];
then
	echo "Welcome $USERNAME"
else
	echo "Invalid username please register an account"
fi

Loops:

#!/bin/bash
#for loops
for NAMES in $(cat names.txt); do
	echo "The name is $NAMES"
done

Functions:

#!/bin/bash
#functions
function shadowtest(){
	if [ -e /etc/shadow ];
	then
		echo "yes it exists"
	else
		echo "Nope"
	fi
}
function testpwd(){
	if [ -e /etc/passwd ];
	then
		echo "yes it exists"
	else
		echo "Nope"
	fi
}
shadowtest
testpwd

Having some fun with Bash:

Manual ping Sweeper:

#!/bin/bash
#ping sweep script
echo "Please enter your subnet: "
read SUBNET
for IP in $(seq 1 254); do 
	ping -c 1 $SUBNET.$IP
done

Password Generator with the SSL Library

#!/bin/bash
#simple password generator
echo "Enter the length of the password: "
read LENGTH 
for P in $(seq 1); 
do
	openssl rand -base64 48 | cut  -c1-$LENGTH
done

File Encryptor/Decryotor:

#!/bin/bash
#file encrypter/decrypter
echo "This is a simple file encrypter/decrypter"
echo "Please choose what you want to do"
choice="Encrypt Decrypt"
select option in $choice; do
	if [ $REPLY = 1 ];
	then
		echo "You have selected encryption"
		echo "Please enter the file name"
		read file;
		gpg -c $file
		echo "The file has been encrypted"

    else
            echo "You have selected decryption"
            echo "Please enter the file name"
            read file2;
            gpg -d $file2
            echo "The file has been decrypted"
        fi
    done

DNS Reverse Lookup:

#!/bin/bash
echo "Please enter your subnet: "
read SUBNET
for IP in $(seq 1 254); do
	dig -x $SUBNET.$ip | grep $IP >> dns.txt;
done

Python Scripting

Basics:

  • If running via command line shabang: #!/bin/python

Variables:

Declaration:

Single value: test = 5
Array: test = [1, dog, 2.5]

Reading User Input:

userInput = input(“Enter a number here: ”)
print(“Your number is: ” + str(userInput))

Conditionals:

if test == true:
   print("It's true!")
elif test == false:
   print("Its false!")
else:
   print("Something is wrong")

Loops:

For loop:

for i in range(0, 5, 1):
 print(i) 
for item in arr:
	print(item)

While loop:

i = 0
while i < 5:
	print(i)
	i = i + 1

Functions:

def firstFun(x, y):
	return x + y


def main():
	variable = firstFun(5, 10)
	print(‘Variable = ’ + str(variable))
main()

The Cool Stuff:

Manual Port Scanner

#!/usr/bin/python3
import socket
host = input("Enter the host: ")
maxport = int(input("Enter the max port to scan: "))
def portScanner():
   for port in range(1, maxport + 1):
       s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
       s.settimeout(10)
       result = s.connect_ex((host, port))
       if result == 0:
           print("Port " + str(port) + " is open")
       s.close()
portScanner()

OS Library:

import os
def main():
    print(os.getcwd())
    # os.chdir("/Users/patrickmccabe/Desktop/")
    # print(os.listdir())
    # os.rmdir("Test1")
    """for dirpath, dirnames, filenames in os.walk("/Users/patrickmccabe/Desktop/"):
        print("Current path:", dirpath)
        print("Directories:", dirnames)
        print("Files:", filenames)
        print()"""
    # print("Home: ", os.environ.get('HOME'))
    # os.path.join(os.environ.get('HOME'), "test.txt")
    print(os.path.basename('/usr/share'))
    print(os.path.dirname('/usr/share'))
    print(os.path.split('/usr/share'))
    print(os.path.exists('/usr/share'))
    print(os.path.isdir('/usr/share'))
    print(os.path.isfile('/usr/share'))
    print(os.path.splitext('/usr/share'))
main()

Some Scapy Fun (Please, please be careful with this and only use it in an environment with permission):

IP Spoof: send(IP(src=“<attacker IP>”, dst=“<target IP>”)/ICMP()/“Hello world”)
Network Sniffing: sniff(iface=“<interface>”, prn=lambda x:x.summary)
BE CAREFUL WITH THIS NEXT ONE
DOS Attack: send(IP(src=“attacker IP”, dst=“<target>”)/TCP(sport=444, dport=444), count=10000)

@pmccabe5

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