Using Impacket/Pcapy with Python 2.6 on Windows

Hello everyone! Today we’ll be installing Impacket and Pcapy for Python 2.6 on Windows. The Impacket module lets you parse network packets, this is very useful for example when developing a sniffer. The Pcapy module interfaces with WinPcap to do the actual packet capture.

From the CORE Security webpage:

What is Impacket?

Impacket is a collection of Python classes focused on providing access to network packets. Impacket allows Python developers to craft and decode network packets in simple and consistent manner. It includes support for low-level protocols such as IP, UDP and TCP, as well as higher-level protocols such as NMB and SMB. Impacket is highly effective when used in conjunction with a packet capture utility or package such as Pcapy. Packets can be constructed from scratch, as well as parsed from raw data. Furthermore, the object oriented API makes it simple to work with deep protocol hierarchies.

What is Pcapy?

Pcapy is a Python extension module that interfaces with the libpcap packet capture library. Pcapy enables python scripts to capture packets on the network. Pcapy is highly effective when used in conjunction with a packet-handling package such as Impacket, which is a collection of Python classes for constructing and dissecting network packets.

There is a problem though – Pcapy hasn’t been updated in quite a while, so there is no MSI installer for Python 2.6. I’ve built it myself and hosted in here in the blog, so you don’t have to. I’ve also built an EXE installer for Impacket, it’s not really needed since it’s a pure Python module, but why not?

So this is the list of files we’ll be needing:

WinPcap_4_1_1.exe

pcapy-0.10.5.win32-py2.6.msi

Impacket-0.9.8.0.win32.exe

Installation is now pretty much straight forward. After running all the installers, let’s try it out with this example script to dump all connection attempts by sniffing SYN packets:

    C:\Documents and Settings\Mario Vilas\Desktop>python connections.py
    Available network interfaces:
            1 - \Device\NPF_GenericDialupAdapter
            2 - \Device\NPF_{5BE055D9-461D-4F51-99DD-188224D1A6D0}
            3 - \Device\NPF_{9B7DC2FB-7660-4E68-B4EC-DB9682C76E40}
            4 - \Device\NPF_{166A618C-4230-42E7-93AD-298D1145F5BC}
            5 - \Device\NPF_{BE987C8D-D523-49B8-8B95-DDDBAA46EB3F}

    Choose an interface [0 to quit]: 2
    Listening on: \Device\NPF_{5BE055D9-461D-4F51-99DD-188224D1A6D0}
    Connection attempt 10.0.2.15 -> 192.168.254.254
    Connection attempt 10.0.2.15 -> 192.168.254.254
    Connection attempt 10.0.2.15 -> 192.168.254.254
    Connection attempt 10.0.2.15 -> 192.168.254.254
    Connection attempt 10.0.2.15 -> 192.168.254.254
    Connection attempt 10.0.2.15 -> 209.85.227.106
    Connection attempt 10.0.2.15 -> 209.85.227.104
    Connection attempt 10.0.2.15 -> 209.85.227.104
    Connection attempt 10.0.2.15 -> 209.85.227.104
    Connection attempt 10.0.2.15 -> 209.85.227.100
    ^C

Below is the source code to the script. Enjoy!

Updates

• A newer version of Impacket is hosted at Google Code, so I built a new installer. The previous version of the installer, based on the version of Impacket found in the Core Security webpage, is still available here: Impacket-0.9.6.0.win32.exe

Download

connections.py

Source code

#!/usr/bin/env python

# Copyright (c) 2009-2010, Mario Vilas
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
#     * Redistributions of source code must retain the above copyright notice,
#       this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright
#       notice,this list of conditions and the following disclaimer in the
#       documentation and/or other materials provided with the distribution.
#     * Neither the name of the copyright holder nor the names of its
#       contributors may be used to endorse or promote products derived from
#       this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
# POSSIBILITY OF SUCH DAMAGE.

from pcapy import findalldevs, open_live
from impacket import ImpactDecoder, ImpactPacket

def get_interface():

    # Get the list of interfaces we can listen on
    ifs = findalldevs()

    # No interfaces found
    if len(ifs) == 0:
        raise RuntimeError, "Error: no available network interfaces, or you don't have enough permissions on this system."

    # A single interface was found
    if len(ifs) == 1:
        interface = ifs[0]

    # Multiple interfaces found
    else:
        print "Available network interfaces:"
        for i in xrange(len(ifs)):
            print '\t%i - %s' % (i + 1, ifs[i])
        print
        while 1:
            choice = raw_input("Choose an interface [0 to quit]: ")
            try:
                i = int(choice)
                if i == 0:
                    interface = None
                    break
                interface = ifs[i-1]
                break
            except Exception:
                pass

    # Return the selected interface
    return interface

def sniff(interface):
    print "Listening on: %s" % interface

    # Open a live capture
    reader = open_live(interface, 1500, 0, 100)

    # Set a filter to be notified only for TCP packets
    reader.setfilter('ip proto \\tcp')

    # Run the packet capture loop
    reader.loop(0, callback)

def callback(hdr, data):

    # Parse the Ethernet packet
    decoder = ImpactDecoder.EthDecoder()
    ether = decoder.decode(data)

    # Parse the IP packet inside the Ethernet packet
    iphdr = ether.child()

    # Parse the TCP packet inside the IP packet
    tcphdr = iphdr.child()

    # Only process SYN packets
    if tcphdr.get_SYN() and not tcphdr.get_ACK():

        # Get the source and destination IP addresses
        src_ip = iphdr.get_ip_src()
        dst_ip = iphdr.get_ip_dst()

        # Print the results
        print "Connection attempt %s -> %s" % (src_ip, dst_ip)

def main():
    interface = get_interface()
    if interface:
        sniff(interface)

if __name__ == "__main__":
    main()