Python Port Scanner

Question

Am newbie to python and stuck at a point. I want to create port scanner with using only python 3 inbuilt libraries (means avoiding scapy etc) I have following code :

import socket
for i in range(1,26): 
 s = socket.socket() 
 s.settimeout(0.5)
 ip = "74.207.244.221" #scanme.nmap.org
 response = s.connect_ex((ip, i)) 
 if response:
 print ("%d\tclose" %i)
 else:
 print ("%d\topen" %i)
 s.close()

Now I want to add 2 functionalities to this : that is

1. Distinguish between close and filtered ports . In both cases am receiving same errno in return so how can I check if I have received back a rst packet or nothing ? As far as I have tried s.recv() isn't working for this.
2. I want to control the number of tries (attempts), i.e I want to send only one or two syn packets. I don't want this program to send more than 2 syn packets for probes. How can this thing be achieved ?

• user2665694: I would expect that every existing port scanner will work much better than code written by a newbie with a reputation of 1.

Answer 1

Distinguish between close and filtered ports . In both cases am receiving same errno in return so how can I check if I have received back a rst packet or nothing

You've probably only checked with servers that send back a RST. Here's what I tried:

• First case, normal config:

  >>> os.strerror(s.connect_ex((ip, 81)))
  'Connection refused'
  

• Second, with manual iptables:

  iptables -A OUTPUT -p tcp --dport 81 -j DROP
  >>> os.strerror(s.connect_ex((ip, 81)))
  'Resource temporarily unavailable'
  

I want to control the number of tries (attempts), i.e I want to send only one or two syn packets.

I don't think there's a setsockopt TCP option exposed, but on linux there's:

net.ipv4.tcp_syn_retries

However, since you limited the timeout for the socket, all operations that don't finish within 0.5 seconds will time out. So it's likely only 1 or 2 SYNs will leave the station.

Answer 2

#!/usr/bin/python
import socket
s = socket.socket(socket.AF_INET, socekt.SOCK_STREAM)
host = 74.207.244.221
def portscan(port):
 try:
 s.connect((host,port))
 return True
 else:
 return False
for x in range(1,255):
 if portscan(x):
 print('Port',x,'Is Open')

• Artem Sokolov: While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.