TCP port testing not accurate with `ip = ipaddress.ip_address(args.ip)`

Question

In this test machine, tcp/80 is listening while tcp/4444 is not. (I already verified this with netstat -an)

If I simply pass args.ip value to ip, and forward it to scan() function, the scan result is always accurate.

ip = args.ip

Normal Output:

C:\>python script.py 127.0.0.1
Port number: 80
Connecting to 127.0.0.1:80
OK 127.0.0.1:80

C:\>python script.py 127.0.0.1
Port number: 4444
Connecting to 127.0.0.1:4444
FAIL 127.0.0.1:4444

C:\>

However, when I try to validate IP Address with the following function

ip = ipaddress.ip_address(args.ip)

the scan result is always wrong.

Wrong Output ... tcp/80 is up and running:

C:\>python script.py 127.0.0.1
Port number: 80
Connecting to 127.0.0.1:80
FAIL 127.0.0.1:80

What's wrong with this code?

import socket, argparse, ipaddress

def main():
    global ip
    parser = argparse.ArgumentParser()
    parser.add_argument('-u')
    group = parser.add_mutually_exclusive_group()
    group.add_argument('-i')
    group.add_argument('ip', nargs='?')
    args = parser.parse_args()
    if args.i:                                      
        print("IP Address is .. " + args.i)
    elif args.ip:                                   
        ip = ipaddress.ip_address(args.ip)          # Prob
        #ip = args.ip                               # OK
        scan()
    elif args.u:
        print("URL is " + args.u)
    else:
        print('No argument provided')

def scan():
    port = input('Port number: ')
    print('Connecting to %s:%s' % (ip,port))    
    try:
        s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.connect((ip, int(port)))
        print('OK %s:%s' % (ip, port))
    except:
        print('FAIL %s:%s' % (ip, port))

main()

Would it be possible to validate the IP Address and then forward it to another function and still getting the correct port scanning test?

Answer 1

You try to pass an IPv4Address instead of a string to s.connect.

It would be more apparent if you didn't use a catch-all except. This is what you get without it:

thierry@amd:~$ python3 test.py 127.0.0.1
Port number: 80
Connecting to 127.0.0.1:80
Traceback (most recent call last):
  File "test.py", line 32, in <module>
    main()
  File "test.py", line 16, in main
    scan()
  File "test.py", line 27, in scan
    s.connect((ip, int(port)))
TypeError: str, bytes or bytearray expected, not IPv4Address

Just use str(ip) instead of ip:

def scan():
    port = input('Port number: ')
    print('Connecting to %s:%s' % (ip,port))    
    try:
        s=socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.connect((str(ip), int(port)))  # ip is an IPv4Address
        print('OK %s:%s' % (ip, port))   # no problem here, str will be used for print
    except ValueError:
        print('FAIL %s:%s' % (ip, port))

---

thierry@amd:~$ python3 test.py 127.0.0.1
Port number: 80
Connecting to 127.0.0.1:80
OK 127.0.0.1:80

You might also want to change your except: into except ConnectionRefusedError: to avoid to catch all exceptions indistinctly.