Netcat Fundamentals

Classification: Host & Network Penetration Testing / Exploitation
Target: demo.ine.local (10.2.30.239)
Attacker: Kali (attackdefense)
Objective: Use Netcat to set up listeners and transfer messages and files between systems.

1. Executive Summary

Netcat (“the TCP/IP swiss army knife”) reads and writes arbitrary TCP/UDP connections. This lab walks through its core uses: probing ports, running listeners, chatting between hosts in both directions, UDP connections, and transferring files.

2. Recon & Help

ping -c 4 demo.ine.local      # 10.2.30.239
nc -h

3. Port Scanning

Connecting to a port tells us if it’s open (80/HTTP) or refused (21/FTP).

nc -nv 10.2.30.239 80         # 80 (http) open
nc -nv 10.2.30.239 21         # 21 (ftp) Connection refused

4. Transferring the Windows nc.exe

Kali ships pre-compiled Windows binaries, including nc.exe.

cd /usr/share/windows-binaries
python -m SimpleHTTPServer 80

5. TCP Listener + Connection

Attacker listens; the target connects in.

nc -nvlp 1234                 # attacker

6. Bidirectional Messaging

Once connected, each side can send lines (messages or commands) to the other — it works both ways.

7. UDP Listener

Add -u for UDP; the client must also specify UDP or the connection fails.

nc -nvlup 1234                # UDP listener
nc -nvu 10.2.30.239 1234      # UDP client

8. File Transfer

Create a file, send it with input redirection, and write it on the receiver with output redirection.

nano example.txt
# receiver:  nc -nvlp 1234 > received.txt
# sender:    nc -nv 10.2.30.239 1234 < example.txt

9. Notes

1. Netcat is a powerful dual-use tool — the same features enable reverse/bind shells and exfiltration, so its presence on production hosts should be restricted/monitored.
2. Prefer ncat (with SSL/auth) over classic nc where encryption or access control matters.