Build your port scanner with built-in libraries in Python

Posted 16 February 2020

This small article will show, how you can build a port scanner with built-in libraries in Python and without need to install external libraries.

Many times when we're performs a troubleshooting or a pentest, we need check if there's connectivity between two hosts. Normally in this process we using tools such as: nmap, NetCat, Telnet, Hping3 e etc. Company's that has a security policy performs a process called "Hardening". It's process consist in remove all unnecessary tools for the purpose of the server.

The script showed here will help you in this task, hence if you are perform a pentest will generate less noise. It will perform a scan type Full Connection, therefore the three handshake will complete. More later in other article, I'll show how we can perform a Stealth Scan, Xmas Scan and others.

Below, I list all libraries use in this script.

The version of Python that was use: 3.8.1

Let's get started!

Main Class

										import sys
import errno
import os
import argparse
import ipaddress

class MyPortScanner(object):

	def __init__(self, target, portlist):
	self.target = target
	if type(portlist) is str:
		self.portlist = [int(x) for x in portlist.split(',')]
	else:
		self.portlist = portlist

In this first part, we just import the necessary libraries and define the class constructor. It'll receive two parameters: target IP and ports. If the user set a port list separeted per comma, we'll generate a list of integers with this port list.

Function for check ports

def check_port_socket_v4_tcp(self):

        print('--------------------------------')
        print('[+] Initializing scan...')
        print('[i] Target host: {}'.format(self.target))
        print('[i] Ports: {}'.format(self.portlist))

        try:
            for port in self.portlist:
                s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                s.settimeout(3)
                result = s.connect_ex((str(self.target), port))

			if result == 0:
				print('[+] Port {}: Open'.format(port))
			else:
				print('[!] Port {}: Closed'.format(port))
				print('\t[-] Code error: {}'.format(errno.errorcode[result]))
				print('\t[-] Message: {}'.format(os.strerror(result)))
			s.close()
		except socket.error as e:
			print(str(e))
			print('[-] Connection Error')
		sys.exit()
		print('[+] Script finished.')

Here our script begins be built. We define the function called "check_port_socket_v4_tcp" that wait a parameter: the class's instance. After this some informations are showed and begins a loop for test all ports in our list portlist. In next line we created a object of class socket with belows parameters: AF_INET == IPv4 and SOCK_STREAM == TCP. After this we set a timeout for 3 seconds and finally we tested the port and save the test result in the result variable.

Lastly we verify the result, if the result is 0 then the port is Open, else is block for any other reasons.

Testing the script

joaopaulo@Joaos-MacBook-Air scanner % python3 sample_port_scanner.py -t 54.207.20.104 -p 80,443,445
--------------------------------
[+] Initializing scan...
[i] Target host: 54.207.20.104
[i] Ports: [80, 443, 445]
[+] Port 80: Open
[+] Port 443: Open
[!] Port 445: Closed
        [-] Code error: EAGAIN
        [-] Message: Resource temporarily unavailable
[+] Script finished.

For test your script, open a CLI session and set 2 parameters: -t for define the target and -p (not required) to define the ports scanned. Below an example: python3 sample_port_scanner.py -t 54.207.20.104 -p 80,443,445

Complete Code

# Import modules
import socket
import sys
import errno
import os
import argparse
import ipaddress

# Main Class
class MyPortScanner(object):

    # Constructor, receive two parameters: target = IP that will be scanned and list of port that will be tested
    def __init__(self, target, portlist):
        self.target = target
        if type(portlist) is str:
            self.portlist = [int(x) for x in portlist.split(',')]
        else:
            self.portlist = portlist

    # Function that performs the scan on v4 family
    def check_port_socket_v4_tcp(self):

        print('--------------------------------')
        print('[+] Initializing scan...')
        print('[i] Target host: {}'.format(self.target))
        print('[i] Ports: {}'.format(self.portlist))

        try:
            for port in self.portlist:
                # Create the v4 socket, AF_INET == V4 Family, SOCK_STREAM == TCP
                s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                # Define the timeout of response to 3 seconds
                s.settimeout(3)
                result = s.connect_ex((str(self.target), port))
                # If the return code is 0 then the port is OPEN
                if result == 0:
                    print('[+] Port {}: Open'.format(port))
                # Otherwise, the port is closed
                else:
                    print('[!] Port {}: Closed'.format(port))
                    print('\t[-] Code error: {}'.format(errno.errorcode[result]))
                    print('\t[-] Message: {}'.format(os.strerror(result)))
                s.close()
        # If have any problem with connection, the scan will be aborted
        except socket.error as e:
            print(str(e))
            print('[-] Connection Error')
            sys.exit()

        print('[+] Script finished.')


# Performs the script
if __name__ == "__main__":
    parser = argparse.ArgumentParser(description='Scan ports TCP\nVersion: 0.1')
    # Target parameter, accept just IPV4 Address
    parser.add_argument('-t', dest='target_host_v4', help='Target host IPv4', required=True, type=ipaddress.IPv4Address)
    # Port that will be scanned, if this parameter not been set then the default ports will be scanned
    parser.add_argument('-p', dest='ports', help='Ports separated by comma', type=str, default=[21, 22, 23, 53, 80, 443,
                                                                                                3389, 389, 3306, 1521,
                                                                                                8080, 8000])
    params = parser.parse_args()
    # Create an instance of MyPortScanner
    m = MyPortScanner(params.target_host_v4, params.ports)
    # Call the function check_port_socket_v4_tcp
    m.check_port_socket_v4_tcp()

Download of the code on GitHub: Sample port scanner

For any questions, send me an email