What is Netcat?

Netcat is a tool used for operations such as scanning data read and write operations between networks on ports using TCP and UDP protocols, in short, port scanning.At its most basic, its function is to read the network.Netcat, which is generally used on the red team side of cyber security, can have serious consequences when used with malicious intent.

Difference between Netcat and Nmap

It is important to know the differences between these two tools, as they are both used mainly for tasks such as port scanning and network reporting.

Netcat is mainly used for networking. While it is used to perform basic network tasks such as establishing a connection between two computers and transferring data, nmap is used to perform network security tests. It performs security-oriented tasks such as scanning a target network, identifying open ports, and identifying services running on the target system.Netcat provides simple and direct data transmission and connection establishment functions. It performs basic network tasks such as data transfer, port listening, and connection establishment.
Nmap, on the other hand, offers a wider range of security tests such as network discovery, port scanning, identifying services running on the target system, and analyzing the target’s vulnerabilities.

There are differences between their usage areas as well as their features.Netcat is basically used for network management and data transfer. For example, when used in scenarios such as file transfer, sending log data, etc.
Nmap is used by security professionals and system administrators for network security testing and reconnaissance. It serves the purpose of identifying weak points in the system and detecting security vulnerabilities.

Systematically Netcat

The Netcat tool was developed in 1996 by a hacker nicknamed Hobbit.This tool, which could only be used on Linux at first, was adapted to Windows over time. Although it comes pre-installed on Linux operating systems such as Kali, sometimes we may need to install this tool manually.

Netcat Installation

To install Netcat, we just need to write a single line command on the command line.

$sudo apt-get install Netcat

When we run the nc -h command, we get an output informing us about the use of nc :

Let’s explain here.

Using Netcat

Netcat tool is represented by ‘nc’ in the linux terminal.Netcat’s Basic Syntax is: nc {options} {host} {port}.

1-)Host

Host is the IP address of the target.

2-)Port

Port is the port number or numbers of the target, more than one port can be listened to.

3-)Options

In Netcad, we can parameterize the operations according to our wishes to get the result we want. To better understand these parameters, we must first know the Client and Listener modes

A-)Listener Mode

• Listener mode allows a computer to listen on a specific port and accept incoming connections.
• The basic usage is as follows:

$ nc -l -p [port]

This command starts listening on the specified port and accepts incoming connections. Listener mode is typically used when a computer is expected to wait for another computer to initiate a connection.

B-)Client Mode

• Client mode allows a computer to establish a connection to a specific target computer over a specified port.
• The basic usage is as follows:

$nc [host] [port]

This command establishes a connection to the specified target host and port. Client mode is commonly used when a computer needs to initiate communication with another computer.

For example, while one computer is running in Listener mode, the other computer can establish a connection by working in Client mode.

eg-

Listener Commant : nc -l -p 12345

Client Commant : nc [listener_bilgisayar_ip] 12345

Now we can learn the parameters

Parameters are mainly as follows:

• -l: (listen mode) listen mode
• -L: (Listen harder) Only valid in Netcat versions prepared for Windows. Even if the client side terminates the connection, it restarts the listening mode. Thus, it turns Netcat into an insistent listener.
• -u: (UDP mode) defaults to TCP. We can use this option to use UDP instead.
• -p:(Local port) This is the option that specifies the listened port when in listen mode and the source port to which all packets will be sent when in client mode.
• -e: If there is a connection, it is the option used to communicate with STDIN and STDOUT when the program runs.
• -n: The option to be used to prevent any change in the names of the other party’s machines in DNS lookups.
• -z: Zero-I/O mode. It means that no data is sent. It is an option used only to send a packet other than the payload.
• -wN: If the connection is timeout, that is, it expires, it waits for another N seconds after STDIN closes. A Netcat client or listener will wait N seconds to open a new connection with this option. If a new connection is not established within this time, Netcat will stop working.
• -v: (Be verbose) This is the option that tells the messages in Standard Error during the connection to be written in detail.
• -vv: (Be very verbose) It is an optional state in Standard Error where it is said to be written in more detail than the -v option.

Netcat Similar Tools

1-)Ncat : Ncat, part of the Nmap project, is an extended version of Netcat. Ncat has capabilities such as various network connections, port listening and data transmission.

2-)Socat : Socat is a network tool that can transfer data between two different communication points. It supports more complex configurations than Netcat.

3-)Hping : Hping is a tool with Netcat-like features and also focuses on packet creation and manipulation capabilities.

4-)Cryptcat : Cryptcat is a version of Netcat with added encrypted communication capabilities. It can be used to provide data encryption and secure communications.

5-)Sbd (Secure Backdoor) : Sbd is a similar tool to Netcat and focuses on encrypted communication capabilities. Can be used to create a secure backdoor.