Nmap, also known as Network Mapper, is a free and open-source tool used by system administrators, network engineers, and security auditors for network discovery and security auditing. Many systems and network administrators also find it useful for tasks such as network inventory, managing service upgrade schedules, and monitoring host or service up-time.
The requirement for administrative rights to use Nmap is related to its function and how it works. Nmap sends specially crafted packets to the target host and then analyzes the responses, to deliver valuable information about the network. For the tool to function at its best performance, it needs to manipulate raw IP packets to perform tasks such as scanning the network, detecting open ports, discovering hosts, and determining the operating system running on a particular system, among other capabilities. But creating and sending raw IP packets is a capability that operating systems usually reserve for privileged users or administrators as a security measure. Therefore, Nmap needs administrative rights (root access) to perform its tasks without any limitations.
An example of this is when Nmap is used to conduct one of its most popular scans – SYN scan (also known as stealth scan). Nmap creates a raw SYN packet (a part of the TCP/IP protocol that is used to initiate a connection between hosts in a network), manipulates the packet details, and then sends it to the target host. If the port is open, the target host replies with a SYN/ACK packet. Nmap, upon receiving the SYN/ACK packet, does not send the expected ACK packet back to the target host, making the attempt ‘uncompleted’ and thereby remaining ‘unnoticed’ or stealthy. This type of operation requires raw socket functionality, which needs administrative rights on most systems.
Detailed information on why administrator rights are needed for Nmap can be found in the Nmap Network Scanning Guide and the official documentation provided by Nmap (Source: https://nmap.org/book/inst-windows.html)
Running Nmap without administrative privileges will limit its capabilities. Some scans may work, but others – particularly the more aggressive and intrusive scans – will either be scaled back or fail entirely.
In conclusion, while it’s possible to run Nmap without administrator rights, it will most likely not provide you with the comprehensive data you need to properly scan and analyze your network. Providing administrative rights enables the tool to fully exploit its network mapping and scanning capabilities.
References:
1. Nmap Network Scanning: Official Nmap Project Guide to Network Discovery and Security Scanning: https://nmap.org/book/man.html
2. Nmap Scanning: The Basics: https://www.linode.com/docs/guides/networking/nmap/.
3. Nmap Cookbook: The Fat-Free Guide to Network Security Scanning: https://www.amazon.com/Nmap-Cookbook-Fat-free-Network-Scanning/dp/1449902529.
