How to use NMAP for penetration testing?

Nmap stands for “Network Mapper”, a free and open-source utility for network discovery and security auditing. Many systems, network administrators, and pentesters also use it to discover hosts and services on a computer network and build a map of the network.

To begin with, you must install Nmap. For Linux systems, the command “sudo apt-get install nmap” will be used. For Windows and Mac systems, the tool can be downloaded from the official Nmap website (https://nmap.org).

The simplest way to use Nmap is to simply run an nmap command followed by a domain name or IP address:

nmap target.com #or nmap 192.168.1.1

This command will run a standard scan against the specified domain or IP address.

But Nmap is not limited to just identifying hosts and their services; it also provides the ability to perform a more detailed scan by using different flags.

1. -p flag: Specifies ports for scanning. For instance, “nmap -p 22,80 target.com” will scan for ports 22 and 80.

1. -A flag: Used for OS detection and version detection. It also tries to determine script scanning and trace route. For example: “nmap -A target.com”.

1. -v flag: Provides verbosity. For instance, “nmap -v target.com”.

1. -sV flag: Probes open ports to determine service/version info. For instance, “nmap -sV target.com”.

1. -O flag: Enables OS detection. For example: “nmap -O target.com”.

These are just a few examples; Nmap has a multitude of scanning options that can be combined, depending on what information you’re seeking to gather during your penetration testing.

However, it’s important to note that while Nmap is a powerful tool in penetration testing, it should ONLY be used for legal and ethical purposes. Unauthorized penetration testing can be deemed illegal and unethical (Joshi, 2013).

For additional commands and usage of Nmap, refer to the official Nmap documentation on the official Nmap website (https://nmap.org/book/man.html) or use the command “nmap -h” to list out all the command options.

One of the great benefits of using Nmap is that it’s widely supported with numerous tutorials and resources available. It’s also continuously updated with new features and improvements, making it a go-to tool for penetration testers.

Reference:
1. Official Nmap website (https://nmap.org/)
2. Joshi, A. (2013). Advanced Penetration Testing for Highly-Secured Environments. Packt Publishing.