Python Ethical Hacking - Intercepting and Modifying Packets

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INTERCEPTING & MODIFYING PACKETS

Scapy can be used to:

Create packets.
Analyze packets.
Send/receive packets.

But it can't be used to intercept packets/flows.

CLASSIC MITM SCENARIO

MITM - SNIFFING DATA

MITM - MODIFYING DATA

1. Execute the command - iptables to capture the packets into a queue.

iptables -I INPUT -d 10.0.0.0/ -j NFQUEUE --queue-num

2. Access the Packets queue.

Install the module netfilterqueue first.

pip3 install -U git+https://github.com/kti/python-netfilterqueue

3. Write the Python script to intercept and process the packets.

#!/usr/bin/env python

from netfilterqueue import NetfilterQueue

def process_packet(packet):

    print(packet)

    packet.accept()

queue = NetfilterQueue()

queue.bind(1, process_packet)

try:

    queue.run()

except KeyboardInterrupt:

    print('')

We can also drop the packets through function packet.drop().

4. Use the following command to stop the packet capturing.

iptables --flush

Converting Packets to Scapy Packets

1. Execute the iptables command to capture the OUTPUT and INPUT packets.

iptables -I OUTPUT -j NFQUEUE --queue-num 

iptables -I INPUT -j NFQUEUE --queue-num

2. Execute the following Python script to process the captured packets.

#!/usr/bin/env python

from netfilterqueue import NetfilterQueue

def process_packet(packet):

    print(packet)

    packet.accept()

queue = NetfilterQueue()

queue.bind(0, process_packet)

try:

    queue.run()

except KeyboardInterrupt:

    print('')

3. Convert the packet to scapy packet and show on the screen.

#!/usr/bin/env python

from netfilterqueue import NetfilterQueue

from scapy.layers.inet import IP

def process_packet(packet):

    scapy_packet = IP(packet.get_payload())

    print(scapy_packet.show())

    packet.accept()

queue = NetfilterQueue()

queue.bind(0, process_packet)

try:

    queue.run()

except KeyboardInterrupt:

    print('')