Nmap Commands: Top 16 Nmap Scan Techniques Explained

Nmap is one of the most popular network mappers in the infosec world. It’s utilized by cybersecurity professionals and newbies alike to audit and discover local and remote open ports, as well as hosts and network information.

Like many OSINT tools, Nmap stands out not only for being open-source but also for being free, multi-platform, and regularly updated each year. Plus, it's one of the most comprehensive tools available for scanning hosts, networks, and ports.

It includes a large set of options to enhance your scanning and mapping tasks, and brings with it an incredible community and comprehensive documentation to help you understand this tool from the very start. Nmap can be used to:

• Create a complete computer network map
• Find remote IP addresses of any hosts
• Get the OS system and software details
• Detects open ports on local and remote systems
• Audit server security standards
• Find vulnerabilities on remote and local hosts

It was mentioned in the OSINT Framework article we published, and today we’ll explore a little bit more about this essential security tool with some practical terminal-based Nmap commands.

What is Nmap?

As we’ve said before, Nmap is a network scanner utility used for port mapping, host discovery and vulnerability scanning. Most of its functions are based on using IP packet analysis to detect and identify remote hosts, operating systems and services.

Nmap is used by mid and large companies as well as smaller-sized organizations for semi-automated and manual port auditing, host monitoring, penetration testing, red and blue team exercises, and similar tasks.

Even with Nmap constantly being updated with new features for decades, its core function remains as a network scanner, helping users gather data by sending packets to local or remote ports. This is done by waiting for packet responses to determine if ports are closed, open or filtered.

The most popular method of using Nmap is via the terminal (command-line console), by performing a Nmap full scan command, but we'll take a look into more examples below.

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How To Use Nmap

Nmap is pretty easy to use if you're familiar with command-line interfaces. As it’s already installed on most Linux/Unix-based distributions, you just have to execute the ‘nmap’ command from any terminal, and that’s it. It will display several options for you.

Advanced users will also be able to use Nmap along with other system scripts and automated tasks in order to maximize the powers of this tool.

Nmap port scan command

One of the most basic Nmap commands for a scan is the nmap port scan command:

That’s how you use Nmap.

How To Install Nmap on Linux, Windows and Mac

What happens if your operating system doesn’t include Nmap? No worries, let’s see how to install it. While the installation process can differ a bit depending on the OS you are using, in most cases (MacOS and Windows) our recommendation is to get the latest release from the Nmap website’s download page.

Installing Nmap on Linux

Open the terminal and run the following commands to get Nmap installed:

• CentOS/Fedora: sudo dnf install nmap
• Ubuntu/Debian: sudo apt-get install nmap

That's it. Nmap is now installed on Linux.

Installing Nmap on Windows

Once you download the installer, execute it and install it. The automated installer should take care of configuring Nmap for you in mere seconds.

Installing Nmap on MacOS

Mac users also have a full automated installer. Just run the Nmap-mpkg file to begin the installation. After a few seconds,

Nmap will be ready on your MacOS.

Nmap Command Examples - Full Tutorial

Let’s get to know a few useful command-line based best Nmap scans that can be performed.

1. Basic Nmap Scan against IP or host

nmap 1.1.1.1

Now, if you want to scan a hostname, simply replace the IP for the host, as you see below:

nmap recordedfuture.xyz

This kind of scans, such as the Nmap scan host are perfect for your first steps when starting with Nmap.

2. Nmap Ping Scan

nmap -sp 192.168.5.0/24

The most famous type of scan is the Nmap ping scan (so-called because it’s often used to perform Nmap ping sweeps), and it’s the easiest way to detect hosts on any network.

The drawback of this ICMP-only type of scan is that remote hosts often block IP-based ping packets, so if you’re unable to get solid results, we recommend switching to ARP-based requests for your scan.

3. Scan specific ports or scan entire port ranges on a local or remote server

nmap -p 1-65535 localhost

In this example, we scanned all 65535 ports for our localhost computer.

Nmap is able to scan all possible ports, but you can also scan specific ports, which will report faster results. See below:

nmap -p 80,443 8.8.8.8

4. Scan multiple IP addresses

Let’s try to scan multiple IP addresses. For this you need to use this syntax:

nmap 1.1.1.1 8.8.8.8

You can also scan consecutive IP addresses:

nmap 1.1.1.1,2,3,4

This will scan 1.1.1.1, 1.1.1.2, 1.1.1.3 and 1.1.1.4.

5. Scan IP ranges

You can also use Nmap to scan entire CIDR IP ranges, for example:

nmap 8.8.8.0/28

This will scan 14 consecutive IP ranges, from 8.8.8.1 to 8.8.8.14.

An alternative is to simply use this kind of range:

nmap 8.8.8.1-14

You can even use wildcards to scan the entire C class IP range, for example:

nmap 8.8.8.*

This will scan 256 IP addresses from 8.8.8.1 to 8.8.8.256.

If you ever need to exclude certain IPs from the IP range scan, you can use the “–exclude” option, as you see below:

nmap -p 8.8.8.* --exclude 8.8.8.1

6. Scan the most popular ports

Using “–top-ports” parameter along with a specific number lets you scan the top X most common ports for that host, as we can see:

nmap --top-ports 20 192.168.1.106

Replace “20” with the desired number. Output example:

[root@securitytrails:~]nmap --top-ports 20 localhost
Starting Nmap 6.40 at 2018-10-01 10:02 EDT
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000016s latency).
Other addresses for localhost (not scanned): 127.0.0.1
PORT STATE SERVICE
21/tcp closed ftp
22/tcp closed ssh
23/tcp closed telnet
25/tcp closed smtp
53/tcp closed domain
80/tcp filtered http
110/tcp closed pop3
111/tcp closed rpcbind
135/tcp closed msrpc
139/tcp closed netbios-ssn
143/tcp closed imap
443/tcp filtered https
445/tcp closed microsoft-ds
993/tcp closed imaps
995/tcp closed pop3s
1723/tcp closed pptp
3306/tcp closed mysql
3389/tcp closed ms-wbt-server
5900/tcp closed vnc
8080/tcp closed http-proxy

7. Scan hosts and IP addresses reading from a text file

In this case, Nmap is also useful to read files that contain hosts and IPs inside.

Let’s suppose you create a list.txt file that contains these lines inside:

192.168.1.106
recordedfuture.xyz
securitytrails.xyz

The “-iL” parameter lets you read from that file, and scan all those hosts for you:

nmap -iL list.txt

8. Save your Nmap scan results to a file

On the other hand, in the following example we will not be reading from a file, but exporting/saving our results into a text file:

nmap -oN output.txt securitytrails.xyz

Nmap has the ability to export files into XML format as well, see the next example:

nmap -oX output.xml securitytrails.xyz

9. Disabling DNS name resolution

If you need to speed up your scans a little bit, you can always choose to disable reverse DNS resolution for all your scans. Just add the “-n” parameter.

[root@securitytrails:~]nmap -p 80 -n 8.8.8.8
Starting Nmap 7.60 at 2018-10-01 09:15 -03
Nmap scan report for 8.8.8.8
Host is up (0.014s latency).
PORT STATE SERVICE
80/tcp filtered http

See the difference with a normal DNS-resolution enabled scan:

[root@securitytrails:~]nmap -p 80 8.8.8.8
Starting Nmap 7.60 at 2018-10-01 09:15 -03
Nmap scan report for google-public-dns-a.google .com (8.8.8.8)
Host is up (0.014s latency).
PORT STATE SERVICE
80/tcp filtered http

10. Scan + OS and service detection with fast execution

Using the “-A” parameter enables you to perform OS and service detection, and at the same time we are combining this with “-T4” for faster execution. See the example below:

nmap -A -T4 securitytrails.xyz

This is the output we got for this test:

11. Detect service/daemon versions

This can be done by using -sV parameters

nmap -sV localhost

As you can see here:

[root@securitytrails:~]nmap -sV localhost
Starting Nmap 7.60 at 2018-10-01 09:28 -03
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000020s latency).
Other addresses for localhost (not scanned): ::1
Not shown: 997 closed ports
PORT STATE SERVICE VERSION
111/tcp open rpcbind 2-4 (RPC #100000)
631/tcp open ipp CUPS 2.2
902/tcp open ssl/vmware-auth VMware Authentication Daemon 1.10 (Uses VNC, SOAP)

Service detection performed. Please report any incorrect results at https:// nmap .org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 7.96 seconds

12. Scan using TCP or UDP protocols

One of the things we love most about Nmap is the fact that it works for both TCP and UDP protocols. And while most services run on TCP, you can also get a great advantage by scanning UDP-based services. Let’s see some examples.

Standard TCP scanning output:

[root@securitytrails:~]nmap -sT 192.168.1.1
Starting Nmap 7.60 at 2018-10-01 09:33 -03
Nmap scan report for 192.168.1.1
Host is up (0.58s latency).
Not shown: 995 closed ports
PORT STATE SERVICE
80/tcp open http
1900/tcp open upnp
20005/tcp open btx
49152/tcp open unknown
49153/tcp open unknown
Nmap done: 1 IP address (1 host up) scanned in 1.43 seconds

UDP scanning results using “-sU” parameter:

[root@securitytrails:~]nmap -sU localhost
Starting Nmap 7.60 at 2018-10-01 09:37 -03
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000021s latency).
Other addresses for localhost (not scanned): ::1
Not shown: 997 closed ports
PORT STATE SERVICE
68/udp open|filtered dhcpc
111/udp open rpcbind
5353/udp open|filtered zeroconf

13. CVE detection using Nmap

One of Nmap’s greatest features that not all the network and systems administrators know about is something called “Nmap Scripting Engine” (known as NSE). This scripting engine allows users to use a pre-defined set of scripts, or write their own using Lua programming language.

Using Nmap scripts is crucial in order to automate system and vulnerability scans. For example, if you want to run a full vulnerability test against your target, you can use these parameters:

nmap -Pn --script vuln 192.168.1.105

Output example:

[root@securitytrails:~]nmap -Pn --script vuln 192.168.1.105
Starting Nmap 7.60 at 2018-10-01 09:46 -03
Pre-scan script results:
| broadcast-avahi-dos:
| Discovered hosts:
| 224.0.0.251
| After NULL UDP avahi packet DoS (CVE-2011-1002).
|_ Hosts are all up (not vulnerable).
Nmap scan report for 192.168.1.105
Host is up (0.00032s latency).
Not shown: 995 closed ports
PORT STATE SERVICE
80/tcp open http
|_http-csrf: Couldn't find any CSRF vulnerabilities.
|_http-dombased-xss: Couldn't find any DOM based XSS.
| http-slowloris-check:
| VULNERABLE:
| Slowloris DOS attack
| State: LIKELY VULNERABLE
| IDs: CVE:CVE-2007-6750
| Slowloris tries to keep many connections to the target web server open and hold
| them open as long as possible. It accomplishes this by opening connections to
| the target web server and sending a partial request. By doing so, it starves
| the http server's resources causing Denial Of Service.
|
| Disclosure date: 2009-09-17
| References:
|_ https:// cve.mitre .org/cgi-bin/cvename.cgi?name=CVE-2007-6750
|_http-stored-xss: Couldn't find any stored XSS vulnerabilities.
|_http-vuln-cve2014-3704: ERROR: Script execution failed (use -d to debug)
1900/tcp open upnp
20005/tcp open btx
49152/tcp open unknown
49153/tcp open unknown

As you can see, in this vulnerability test we were able to detect one CVE (Slowloris DOS attack).

14. Flood testing with Nmap

Nmap features never seem to end, and thanks to the NSE, that even allows us to launch flood attacks against our network to test how effective our mitigation methods are.

In our previous example (#12) we found the host was vulnerable to Slowloris attack, and now we’ll try to exploit that vulnerability by launching a flood attack in a forever loop:

nmap 192.168.1.105 -max-parallelism 800 -Pn --script http-slowloris --script-args http-slowloris.runforever=true

15. Testing brute force attacks

NSE is really fascinating -- it contains scripts for everything you can imagine. See the next three examples of BFA against WordPress, MSSQL, and FTP server:

nmap -sV --script http-wordpress-brute --script-args 'userdb=users.txt,passdb=passwds.txt,http-wordpress-brute.hostname=domain.xyz, http-wordpress-brute.threads=3,brute.firstonly=true' 192.168.1.105

WordPress brute force attack:

nmap -p 1433 --script ms-sql-brute --script-args userdb=customuser.txt,passdb=custompass.txt 192.168.1.105

Brute force attack against MS-SQL:

nmap -p 1433 --script ms-sql-brute --script-args userdb=customuser.txt,passdb=custompass.txt 192.168.1.105

FTP brute force attack:

nmap --script ftp-brute -p 21 192.168.1.105

16. Detecting malware infections on remote hosts

Nmap is able to detect malware and backdoors by running extensive tests on a few popular OS services like Identd, Proftpd, Vsftpd, IRC, SMB, and SMTP. It also has a module to check for popular malware signs inside remote servers and integrates Google’s Safe Browsing and VirusTotal databases as well.

A common malware scan can be performed by using:

nmap -sV --script=http-malware-host 192.168.1.105

Or using Google’s Malware check:

nmap -p80 --script http-google-malware infectedsite.xyz

Output example:

Nmap is one of the most complete and accurate port scanners used by infosec professionals today. With it, you can perform simple port scan tasks or use its powerful scripting engine to launch DOS attacks, detect malware or brute force testing on remote and local servers.

Today we covered the top fifteen Nmap commands to scan remote hosts, but there’s a lot more to discover if you’re starting to use Nmap in your OSINT strategy.

Nmap FAQ

Nmap has been one of the most popular port and network scanners for decades. Still, new users often have questions about how it works and its legal usage, and even look for other, similar software from time to time.

Is Nmap free?

Yes, Nmap is completely free for you to download and use. It’s also an open source (licensed) project, so you can inspect, modify, and enhance it to match your needs.

Is Nmap Legal?

Nmap is legal; however, that hinges entirely on the purpose the user has for using it. Scanning your own network is totally legal, but scanning third-party networks may get you into legal problems if you aren’t authorized, depending on the country and state in which you live.

There are many nuances to—and opinions about—port scanning legality. To help you avoid legal issues, we recommend reading the official implications detailed on the Nmap website’s legal issues page.

How Does it Work?

Nmap works by sending and receiving network packets, and checking against its fingerprint database and other methods, to quickly detect hosts and IP addresses over a network. It then performs analysis on the data to quickly respond with results on your console. Most Nmap scans will require you to perform them with root-based (admin) access on Linux and Unix. While on Windows, running Nmap with an administrator account is always a good practice.

Is there any other similar software like Nmap?

There are tons of alternatives to Nmap, including Masscan, Rustcan, and others. While some of this similar software offers faster scanning times, almost none of them offers as many options and high-quality results as an Nmap full scan does.

For most users, even the advanced ones, Nmap is enough. If you don’t like terminals, you can always take a look into ZenMap, the GUI-based version of Nmap.

Wrapping up

Understanding network security and threat intelligence is crucial, but the reliance on manual scans can be time-consuming and less efficient than needed. These traditional methods, while foundational, are time-consuming and can divert resources from strategic initiatives. The evolution of cybersecurity threats demands a more efficient approach.

This is where Recorded Future steps in. Our intelligence platform cuts through the noise and saves you from the time sink of manual processes. Ready to see the difference for yourself?. Take your efforts to the next level—book a demo today.