Nmap Cheat Sheet

Nmap has a multitude of options and when you first start playing with this excellent tool it can be a bit daunting. In this cheat sheet you will find a series of practical example commands for running Nmap and getting the most of this powerful tool.

Keep in mind that this cheat sheet merely touches the surface of the available options. The Nmap Documentation portal is your reference for digging deeper into the options available.

Nmap Target Selection

Scan a single IP nmap
Scan a host nmap www.testhostname.com
Scan a range of IPs nmap
Scan a subnet nmap
Scan targets from a text file nmap -iL list-of-ips.txt

These are all default scans, which will scan 1000 TCP ports. Host discovery will take place.

Nmap Port Selection

Scan a single Port nmap -p 22
Scan a range of ports nmap -p 1-100
Scan 100 most common ports (Fast) nmap -F
Scan all 65535 ports nmap -p-

Nmap Port Scan types

Scan using TCP connect nmap -sT
Scan using TCP SYN scan (default) nmap -sS
Scan UDP ports nmap -sU -p 123,161,162
Scan selected ports - ignore discovery nmap -Pn -F

Privileged access is required to perform the default SYN scans. If privileges are insufficient a TCP connect scan will be used. A TCP connect requires a full TCP connection to be established and therefore is a slower scan. Ignoring discovery is often required as many firewalls or hosts will not respond to PING, so could be missed unless you select the -Pn parameter. Of course this can make scan times much longer as you could end up sending scan probes to hosts that are not there.

Take a look at the Nmap Tutorial for a detailed look at the scan process.

Service and OS Detection

Detect OS and Services nmap -A
Standard service detection nmap -sV
More aggressive Service Detection nmap -sV --version-intensity 5
Lighter banner grabbing detection nmap -sV --version-intensity 0

Service and OS detection rely on different methods to determine the operating system or service running on a particular port. The more aggressive service detection is often helpful if there are services running on unusual ports. On the other hand the lighter version of the service will be much faster as it does not really attempt to detect the service simply grabbing the banner of the open service.

Nmap Output Formats

Save default output to file nmap -oN outputfile.txt
Save results as XML nmap -oX outputfile.xml
Save results in a format for grep nmap -oG outputfile.txt
Save in all formats nmap -oA outputfile

The default format could also be saved to a file using a simple file redirect command > file. Using the -oN option allows the results to be saved but also can be monitored in the terminal as the scan is under way.

Digging deeper with NSE Scripts

Scan using default safe scripts nmap -sV -sC
Get help for a script nmap --script-help=ssl-heartbleed
Scan using a specific NSE script nmap -sV -p 443 –script=ssl-heartbleed.nse
Scan with a set of scripts nmap -sV --script=smb*

According to my Nmap install there are currently 471 NSE scripts. The scripts are able to perform a wide range of security related testing and discovery functions. If you are serious about your network scanning you really should take the time to get familiar with some of them.

The option --script-help=$scriptname will display help for the individual scripts. To get an easy list of the installed scripts try locate nse | grep script.

You will notice I have used the -sV service detection parameter. Generally most NSE scripts will be more effective and you will get better coverage by including service detection.

A scan to search for DDOS reflection UDP services

Scan for UDP DDOS reflectors nmap –sU –A –PN –n –pU:19,53,123,161 –script=ntp-monlist,dns-recursion,snmp-sysdescr

UDP based DDOS reflection attacks are a common problem that network defenders come up against. This is a handy Nmap command that will scan a target list for systems with open UDP services that allow these attacks to take place. Full details of the command and the background can be found on the Sans Institute Blog where it was first posted.

HTTP Service Information

Gather page titles from HTTP services nmap --script=http-title
Get HTTP headers of web services nmap --script=http-headers
Find web apps from known paths nmap --script=http-enum

There are many HTTP information gathering scripts, here are a few that are simple but helpful when examining larger networks. Helps in quickly identifying what the HTTP service is that is running on the open port. Note the http-enum script is particularly noisy. It is similar to Nikto in that it will attempt to enumerate known paths of web applications and scripts. This will inevitably generated hundreds of 404 HTTP responses in the web server error and access logs.

Detect Heartbleed SSL Vulnerability

Heartbleed Testing nmap -sV -p 443 --script=ssl-heartbleed

Heartbleed detection is one of the available SSL scripts. It will detect the presence of the well known Heartbleed vulnerability in SSL services. Specify alternative ports to test SSL on mail and other protocols (Requires Nmap 6.46).

IP Address information

Find Information about IP address nmap --script=asn-query,whois,ip-geolocation-maxmind

Gather information related to the IP address and netblock owner of the IP address. Uses ASN, whois and geoip location lookups. See the IP Tools for more information and similar IP address and DNS lookups.

Remote Scanning

Testing your network perimeter from an external perspective is key when you wish to get the most accurate results. By assessing your exposure from the attackers perspective you can validate firewall rule audits and understand exactly what is allowed into your network. This is the reason we offer a hosted or online version of the Nmap port scanner. To enable remote scanning easily and effectively because anyone who has played with shodan.io knows very well how badly people test their perimeter networks.

Additional Resources

The above commands are just a taste of the power of Nmap. Check out the full set of features by running Nmap with no options. The creator of Nmap Fyodor has a book available that covers the tool in depth. You could also check out our Nmap Tutorial that has more information and tips.

HackerTarget.com offers a hosted version of Nmap that allows you to port scan any Internet facing IP address or range of addresses.

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