NMAP: commands

Nmap Target Selection

Scan a single IP	nmap 192.168.1.1
Scan a host	nmap www.testhostname.com
Scan a range of IPs	nmap 192.168.1.1-20
Scan a subnet	nmap 192.168.1.0/24
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 22 192.168.1.1
Scan a range of ports	nmap -p 1-100 192.168.1.1
Scan 100 most common ports (Fast)	nmap -F 192.168.1.1
Scan all 65535 ports	nmap -p- 192.168.1.1

Nmap Port Scan types

Scan using TCP connect	nmap -sT 192.168.1.1
Scan using TCP SYN scan (default)	nmap -sS 192.168.1.1
Scan UDP ports	nmap -sU -p 123,161,162 192.168.1.1
Scan selected ports - ignore discovery	nmap -Pn -F 192.168.1.1

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 192.168.1.1
Standard service detection	nmap -sV 192.168.1.1
More aggressive Service Detection	nmap -sV --version-intensity 5 192.168.1.1
Lighter banner grabbing detection	nmap -sV --version-intensity 0 192.168.1.1

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 192.168.1.1
Save results as XML	nmap -oX outputfile.xml 192.168.1.1
Save results in a format for grep	nmap -oG outputfile.txt 192.168.1.1
Save in all formats	nmap -oA outputfile 192.168.1.1

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 192.168.1.1
Get help for a script	nmap --script-help=ssl-heartbleed
Scan using a specific NSE script	nmap -sV -p 443 –script=ssl-heartbleed.nse 192.168.1.1
Scan with a set of scripts	nmap -sV --script=smb* 192.168.1.1

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 192.168.1.0/24

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 192.168.1.0/24
Get HTTP headers of web services	nmap --script=http-headers 192.168.1.0/24
Find web apps from known paths	nmap --script=http-enum 192.168.1.0/24

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 192.168.1.0/24

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 192.168.1.0/24

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

Depending on network perimeter you are scanning remember scanning Internet resources from an external perspective is key when assessing your exposure. 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.