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McSniff

Packet sniffer and interpreter... you know for research purposes

Reasoning

I wanted to literally dig into the payloads, frames, packets etc. of what's actually going back and forth over a network. Understanding the breakdown of the structure, byte-for-byte was a good learning experience.

I know, I know, I can just use scapy or use WireShark and dig into them, but where's the fun in that!?

Notes

  1. Example below of how to do the same in scapy
  2. For a deep dive into ethernet frames, see this great resource

Features and functionality

Tool features

  • Listen on different interfaces
  • Track statistics (start/end time, counts of frames/packets/etc.)
  • All the things listed below under OSI layers

OSI layers

Broken down into the OSI model layers, this tool can process/dump/inspect the following:

L2 - Data Link Layer

  • Ethernet frame(s)
  • ARP/RARP packet(s)?
    • Contention as technically not but also L2.5 depending who you ask lol

L3 - Network Layer

  • IPv4 packet(s)
  • IPv6 packet(s)
  • ICMP packets(s)
  • ICMPv6 packets(s)
  • IGMP packet(s)

L4 - Transport Layer

  • TCP segment(s)
  • UDP datagram(s)

Run

TL;DR

Minimum input required is the interface to listen on

sudo python McSniff.py <interface>

# example
sudo python McSniff.py eth0

Help

Using the -h flag will output the below for all options and params that can be supplied

~ sudo python McSniff.py -h
usage: McSniff.py [-h] [-p] [-s] [-t] [-2 [{ETH,ARP,RARP} ...]] [-3 [{IPv4,IPv6,ICMP,ICMPv6,IGMP} ...]] [-4 [{TCP,UDP} ...]] interface

Network analyser (packet sniffer)... for you know, research purposes ;)

positional arguments:
  interface             interface to analyse, run 'ip link' to list

options:
  -h, --help            show this help message and exit
  -p, --payload         dump payload output
  -s, --stats           enable and show statistics for what's been processed
  -t, --https           include dumps even for 443 port payloads (encrypted traffic)
  -2 [{ETH,ARP,RARP} ...], --level2 [{ETH,ARP,RARP} ...]
                        OSI level 2 filter, by default listens for all, supply no args to ignore level
  -3 [{IPv4,IPv6,ICMP,ICMPv6,IGMP} ...], --level3 [{IPv4,IPv6,ICMP,ICMPv6,IGMP} ...]
                        OSI level 3 filter, by default listens for all, supply no args to ignore level
  -4 [{TCP,UDP} ...], --level4 [{TCP,UDP} ...]
                        OSI level 4 filter, by default listens for all, supply no args to ignore level

Examples

What you supply when toggling the levels is what you get, i.e. you supply only IPv4 you get only IPv4. Also a little bit of common sense is required, for example if you specify nothing for -3 you won't get anything for L4 (TCP/UDP) as it's nested within L3!

Capture only frames, don't look deeper

sudo python McSniff.py eth0 -2 ETH

Capture only IPv4 and IPv6, ignoring ARP/RARP, ICMP etc.

sudo python McSniff.py eth0 -2 ETH -3 IPv4 IPv6

Capture only IPv6 UDP packets, dump payload and enable statistics

sudo python McSniff.py eth0 -2 ETH -3 IPv6 -4 UDP -p -s

Run whilst working on script

while true; clear; echo 'Running...'; do sudo timeout 20 python McSniff.py eth0; echo 'Sleeping...'; sleep 5; done

Triggering payloads

L2

# eth - be connected to a network

# arp
sudo arping <destination>

# rarp - not really seen, can happen during boot but DCHP superseeded it

L3

# ICMP (v4)
ping -4 <destination>
ping -4 google.co.uk

# ICMPv6 - need to have IPv6 enabled on interface ofc
ping -6 <destination>
ping -6 google.co.uk

L4

# TCP - unsecure HTTP requests are great as you can see the payload, HTTPS is encrypted so you can't see payload (unless you have the certs to decrypt)
curl http://<destination>

# -k means ignore certs/verification, connect anyway
curl -k http://httpforever.com/

# UDP - DNS requests are easiest to trigger
dig <host>
dig google.co.uk

# to force the query to a specific name server, specify the @ flag
dig @<name server like 1.1.1.1> <host>
dig @1.1.1.1 google.co.uk

Further reading/docs

  1. Python struct formatting
  2. Python socket docs
  3. Ethernet frame Wiki
  4. EtherType Wiki
  5. IPv4 packet structure Wiki
  6. IP protocol numbers Wiki
  7. UDP structure Wiki
  8. TCP strcuture Wiki
  9. Ping (ICMP/ICMPv6) structure Wiki
  10. ARP structure Wiki

Example from scapy

from scapy.all import sniff
sniff(iface="eth0", prn=lambda x: x.show())