Python Ethical Hacking - Intercepting and Modifying Packets

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('')

4. Stop the capture of the packet by the command.

iptables --flush