To build a custom MSN Protocol packet sniffer in Python, you must focus on intercepting TCP traffic on port 1863 and parsing the plain-text, command-based MSNP architecture. The MSN Messenger protocol (MSNP) is inherently a text-based, command-driven protocol where commands are sent as three-letter capitalized words (e.g., VER, USR, MSG) followed by arguments and transaction IDs.
The most efficient and robust way to construct this tool is by using the Scapy Library. Prerequisites
You need administrative privileges to run a packet sniffer since it requires placing your network interface into promiscuous mode. Install Scapy via pip: pip install scapy Use code with caution. Step-by-Step Implementation 1. Target the Architecture MSN Protocol traditionally relies on a distinct workflow: Port: TCP port 1863 (standard MSNP port). Command Format: CMD [Transaction_ID] [Arguments]
Payload Commands: Commands like MSG (Instant Messages) have a payload length field specified in their arguments, followed by the actual message block. 2. Python Sniffer Script
This custom script hooks into Scapy’s sniff loop, isolates TCP traffic communicating on port 1863, filters out background network layers, and extracts clear-text MSN commands.
from scapy.all import sniff, TCP, IP import sys def parse_msn_packet(packet): “”“Callback function to parse captured MSN protocol data.”“” # Ensure the packet contains both IP and TCP layers if packet.haslayer(IP) and packet.haslayer(TCP): # Filter for the MSN Messenger default port (1863) if packet[TCP].sport == 1863 or packet[TCP].dport == 1863: # Check if there is actual application data payload if packet[TCP].payload: raw_payload = bytes(packet[TCP].payload) try: # MSN Protocol commands are text-based ASCII strings text_payload = raw_payload.decode(‘utf-8’, errors=‘ignore’) # Log the basic connection info src_ip = packet[IP].src dst_ip = packet[IP].dst print(f” [+] MSN Traffic Captured: {src_ip} -> {dst_ip}“) # Split into lines to extract MSNP commands lines = text_payload.split(’ ‘) for line in lines: if not line.strip(): continue # Parse known MSNP command structures parts = line.split(’ ‘) command = parts[0] if command in [‘VER’, ‘INF’, ‘USR’, ‘CAL’, ‘JOI’, ‘BYE’]: print(f” -> Protocol Command: {line}“) elif command == ‘MSG’: print(f” -> [MESSAGE ENVELOPE]: {line}“) elif “Content-Type:” in line or “X-MMS-IM-Format:” in line: # Catch metadata fields of a message block print(f” Header info: {line}“) else: # Print text payload line if it resembles conversation if len(line) > 0 and not command.isupper(): print(f” Text Content: {line}“) except Exception as e: # Gracefully skip unparseable binary streams (e.g., file transfers) pass def main(): print(”[] Starting Custom MSN Protocol Sniffer…“) print(”[] Listening on TCP port 1863. Press Ctrl+C to stop.“) try: # BPF Filter targets only TCP traffic on port 1863 sniff(filter=“tcp port 1863”, prn=parse_msn_packet, store=0) except KeyboardInterrupt: print(” [*] Sniffer stopped.“) sys.exit(0) except PermissionError: print(” [!] Error: Root/Administrator privileges required to sniff raw sockets.“) sys.exit(1) if name == “main”: main() Use code with caution. Core Components Explained
filter=“tcp port 1863”: Uses Berkeley Packet Filter (BPF) syntax directly inside Scapy’s engine. This ensures your Python script does not waste CPU cycles analyzing unrelated network noise like HTTPS or DNS traffic.
store=0: Tells Scapy not to hold captured packets inside system RAM. This prevents memory leaks and crashes if you leave the sniffer running over long observation windows.
.decode(‘utf-8’, errors=‘ignore’): Safely translates raw TCP byte data into human-readable text. It drops invalid characters without throwing exceptions when processing occasional binary data like profile icons or file handshakes. Common MSN Protocol (MSNP) Signatures to Look For
When observing your sniffer output, look for these specific text commands to verify your parser is working correctly: Definition What it looks like VER Protocol Version Negotiation VER 1 TR0 MSNP15 MSNP10 USR User Authentication/Identification USR 2 TWN I [email protected] JOI User Joins Chat Session JOI [email protected] Nickname MSG Chat Message Delivery MSG [email protected] Nickname 134 (followed by length)
If you are expanding this sniffer into an analyzer tool, you can implement state tracking to track the transaction IDs (the numbers following the commands) to stitch together full user chat sessions. Usage — Scapy 2.7.1 documentation
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