- Nmap (Network Mapper) is a security scanning, monitoring and evaluation tool for a network system developed by Gordon Lyon (also known as Fyodor Vaskovich).
- Nmap was first published in September 1997.
- Nmap is free and open source software, initially developed only on Linux platform, then developed on many different platforms such as Windows, Solari, Mac OS… and developed more user interface versions ( Zenmap).
Functions of Nmap:
- Detect hosts (which are computers or devices) operating on the network environment.
- Lists open ports (network service ports) on a host.
- Identify services that run on open ports along with the software and version in use.
- Identify the device’s operating system.
- Run special scripts.
Install Nmap
On Windows go to https://nmap.org and download the latest version, install it like normal software.
On Linux (Debian) can be installed from the Repository (repository) with the command:
sudo apt-get install nmapOn Linux (Red Hat) can be installed from the Repository
sudo yum install nmapOn macOS it can be installed via homebrew (need to install homebrew first) and with the command:
sudo brew install nmap
Nmap runs under the command line interface, on Windows open “cmd” on Linux and macOS open “Terminal” and type the command “nmap”
Nmap provides many command parameters to perform the scan, so it is necessary to define the necessary information in advance and apply the appropriate command parameters to perform the scan. Some examples of nmap cheatsheet:
Target Specification
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| nmap 192.168.1.1 | Scan a single IP | |
| nmap 192.168.1.1 192.168.2.1 | Scan specific IPs | |
| nmap 192.168.1.1-254 | Scan a range | |
| nmap scanme.nmap.org | Scan a domain | |
| nmap 192.168.1.0/24 | Scan using CIDR notation | |
| -iL | nmap -iL targets.txt | Scan targets from a file |
| -iR | nmap -iR 100 | Scan 100 random hosts |
| –exclude | nmap –exclude 192.168.1.1 | Exclude listed hosts |
Nmap Scan Techniques
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -sS | nmap 192.168.1.1 -sS | TCP SYN port scan (Default) |
| -sT | nmap 192.168.1.1 -sT | TCP connect port scan (Default without root privilege) |
| -sU | nmap 192.168.1.1 -sU | UDP port scan |
| -sA | nmap 192.168.1.1 -sA | TCP ACK port scan |
| -sW | nmap 192.168.1.1 -sW | TCP Window port scan |
| -sM | nmap 192.168.1.1 -sM | TCP Maimon port scan |
Host Discovery
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -sL | nmap 192.168.1.1-3 -sL | No Scan. List targets only |
| -sn | nmap 192.168.1.1/24 -sn | Disable port scanning. Host discovery only. |
| -Pn | nmap 192.168.1.1-5 -Pn | Disable host discovery. Port scan only. |
| -PS | nmap 192.168.1.1-5 -PS22-25,80 | TCP SYN discovery on port x. Port 80 by default |
| -PA | nmap 192.168.1.1-5 -PA22-25,80 | TCP ACK discovery on port x. Port 80 by default |
| -PU | nmap 192.168.1.1-5 -PU53 | UDP discovery on port x. Port 40125 by default |
| -PR | nmap 192.168.1.1-1/24 -PR | ARP discovery on local network |
| -n | nmap 192.168.1.1 -n | Never do DNS resolution |
Nmap Command Generator
Say goodbye to the hassle of trying to remember the exact syntax for your Nmap commands! With our Nmap Command Generator, you can simply say what you need Nmap to do and we will generate the command for you.
Port Specification
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -p | nmap 192.168.1.1 -p 21 | Port scan for port x |
| -p | nmap 192.168.1.1 -p 21-100 | Port range |
| -p | nmap 192.168.1.1 -p U:53,T:21-25,80 | Port scan multiple TCP and UDP ports |
| -p | nmap 192.168.1.1 -p- | Port scan all ports |
| -p | nmap 192.168.1.1 -p http,https | Port scan from service name |
| -F | nmap 192.168.1.1 -F | Fast port scan (100 ports) |
| –top-ports | nmap 192.168.1.1 –top-ports 2000 | Port scan the top x ports |
| -p-65535 | nmap 192.168.1.1 -p-65535 | Leaving off initial port in range makes the scan start at port 1 |
| -p0- | nmap 192.168.1.1 -p0- | Leaving off end port in range makes the scan go through to port 65535 |
Service and Version Detection
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -sV | nmap 192.168.1.1 -sV | Attempts to determine the version of the service running on port |
| -sV –version-intensity | nmap 192.168.1.1 -sV –version-intensity 8 | Intensity level 0 to 9. Higher number increases possibility of correctness |
| -sV –version-light | nmap 192.168.1.1 -sV –version-light | Enable light mode. Lower possibility of correctness. Faster |
| -sV –version-all | nmap 192.168.1.1 -sV –version-all | Enable intensity level 9. Higher possibility of correctness. Slower |
| -A | nmap 192.168.1.1 -A | Enables OS detection, version detection, script scanning, and traceroute |
OS Detection
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -O | nmap 192.168.1.1 -O | Remote OS detection using TCP/IP stack fingerprinting |
| -O –osscan-limit | nmap 192.168.1.1 -O –osscan-limit | If at least one open and one closed TCP port are not found it will not try OS detection against host |
| -O –osscan-guess | nmap 192.168.1.1 -O –osscan-guess | Makes Nmap guess more aggressively |
| -O –max-os-tries | nmap 192.168.1.1 -O –max-os-tries 1 | Set the maximum number x of OS detection tries against a target |
| -A | nmap 192.168.1.1 -A | Enables OS detection, version detection, script scanning, and traceroute |
Timing and Performance
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -T0 | nmap 192.168.1.1 -T0 | Paranoid (0) Intrusion Detection System evasion |
| -T1 | nmap 192.168.1.1 -T1 | Sneaky (1) Intrusion Detection System evasion |
| -T2 | nmap 192.168.1.1 -T2 | Polite (2) slows down the scan to use less bandwidth and use less target machine resources |
| -T3 | nmap 192.168.1.1 -T3 | Normal (3) which is default speed |
| -T4 | nmap 192.168.1.1 -T4 | Aggressive (4) speeds scans; assumes you are on a reasonably fast and reliable network |
| -T5 | nmap 192.168.1.1 -T5 | Insane (5) speeds scan; assumes you are on an extraordinarily fast network |
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Timing and Performance Switches
| SWITCH | EXAMPLE INPUT | DESCRIPTION |
|---|---|---|
| –host-timeout <time> | 1s; 4m; 2h | Give up on target after this long |
| –min-rtt-timeout/max-rtt-timeout/initial-rtt-timeout <time> | 1s; 4m; 2h | Specifies probe round trip time |
| –min-hostgroup/max-hostgroup <size<size> | 50; 1024 | Parallel host scan group sizes |
| –min-parallelism/max-parallelism <numprobes> | 10; 1 | Probe parallelization |
| –max-retries <tries> | 3 | Specify the maximum number of port scan probe retransmissions |
| –min-rate <number> | 100 | Send packets no slower than <number> per second |
| –max-rate <number> | 100 | Send packets no faster than <number> per second |
NSE Scripts
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -sC | nmap 192.168.1.1 -sC | Scan with default NSE scripts. Considered useful for discovery and safe |
| –script default | nmap 192.168.1.1 –script default | Scan with default NSE scripts. Considered useful for discovery and safe |
| –script | nmap 192.168.1.1 –script=banner | Scan with a single script. Example banner |
| –script | nmap 192.168.1.1 –script=http* | Scan with a wildcard. Example http |
| –script | nmap 192.168.1.1 –script=http,banner | Scan with two scripts. Example http and banner |
| –script | nmap 192.168.1.1 –script “not intrusive” | Scan default, but remove intrusive scripts |
| –script-args | nmap –script snmp-sysdescr –script-args snmpcommunity=admin 192.168.1.1 | NSE script with arguments |
Useful NSE Script Examples
| COMMAND | DESCRIPTION |
|---|---|
| nmap -Pn –script=http-sitemap-generator scanme.nmap.org | http site map generator |
| nmap -n -Pn -p 80 –open -sV -vvv –script banner,http-title -iR 1000 | Fast search for random web servers |
| nmap -Pn –script=dns-brute domain.com | Brute forces DNS hostnames guessing subdomains |
| nmap -n -Pn -vv -O -sV –script smb-enum*,smb-ls,smb-mbenum,smb-os-discovery,smb-s*,smb-vuln*,smbv2* -vv 192.168.1.1 | Safe SMB scripts to run |
| nmap –script whois* domain.com | Whois query |
| nmap -p80 –script http-unsafe-output-escaping scanme.nmap.org | Detect cross site scripting vulnerabilities |
| nmap -p80 –script http-sql-injection scanme.nmap.org | Check for SQL injections |
Firewall / IDS Evasion and Spoofing
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -f | nmap 192.168.1.1 -f | Requested scan (including ping scans) use tiny fragmented IP packets. Harder for packet filters |
| –mtu | nmap 192.168.1.1 –mtu 32 | Set your own offset size |
| -D | nmap -D 192.168.1.101,192.168.1.102,192.168.1.103,192.168.1.23 192.168.1.1 | Send scans from spoofed IPs |
| -D | nmap -D decoy-ip1,decoy-ip2,your-own-ip,decoy-ip3,decoy-ip4 remote-host-ip | Above example explained |
| -S | nmap -S www.microsoft.com www.facebook.com | Scan Facebook from Microsoft (-e eth0 -Pn may be required) |
| -g | nmap -g 53 192.168.1.1 | Use given source port number |
| –proxies | nmap –proxies http://192.168.1.1:8080, http://192.168.1.2:8080 192.168.1.1 | Relay connections through HTTP/SOCKS4 proxies |
| –data-length | nmap –data-length 200 192.168.1.1 | Appends random data to sent packets |
Example IDS Evasion command
nmap -f -t 0 -n -Pn –data-length 200 -D
192.168.1.101,192.168.1.102,192.168.1.103,192.168.1.23 192.168.1.1
Output
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -oN | nmap 192.168.1.1 -oN normal.file | Normal output to the file normal.file |
| -oX | nmap 192.168.1.1 -oX xml.file | XML output to the file xml.file |
| -oG | nmap 192.168.1.1 -oG grep.file | Grepable output to the file grep.file |
| -oA | nmap 192.168.1.1 -oA results | Output in the three major formats at once |
| -oG – | nmap 192.168.1.1 -oG – | Grepable output to screen. -oN -, -oX – also usable |
| –append-output | nmap 192.168.1.1 -oN file.file –append-output | Append a scan to a previous scan file |
| -v | nmap 192.168.1.1 -v | Increase the verbosity level (use -vv or more for greater effect) |
| -d | nmap 192.168.1.1 -d | Increase debugging level (use -dd or more for greater effect) |
| –reason | nmap 192.168.1.1 –reason | Display the reason a port is in a particular state, same output as -vv |
| –open | nmap 192.168.1.1 –open | Only show open (or possibly open) ports |
| –packet-trace | nmap 192.168.1.1 -T4 –packet-trace | Show all packets sent and received |
| –iflist | nmap –iflist | Shows the host interfaces and routes |
| –resume | nmap –resume results.file | Resume a scan |
Helpful Nmap Output examples
| COMMAND | DESCRIPTION |
|---|---|
| nmap -p80 -sV -oG – –open 192.168.1.1/24 | grep open | Scan for web servers and grep to show which IPs are running web servers |
| nmap -iR 10 -n -oX out.xml | grep “Nmap” | cut -d ” ” -f5 > live-hosts.txt | Generate a list of the IPs of live hosts |
| nmap -iR 10 -n -oX out2.xml | grep “Nmap” | cut -d ” ” -f5 >> live-hosts.txt | Append IP to the list of live hosts |
| ndiff scanl.xml scan2.xml | Compare output from nmap using the ndif |
| xsltproc nmap.xml -o nmap.html | Convert nmap xml files to html files |
| grep ” open ” results.nmap | sed -r ‘s/ +/ /g’ | sort | uniq -c | sort -rn | less | Reverse sorted list of how often ports turn up |
Miscellaneous Nmap Flags
| SWITCH | EXAMPLE | DESCRIPTION |
|---|---|---|
| -6 | nmap -6 2607:f0d0:1002:51::4 | Enable IPv6 scanning |
| -h | nmap -h | nmap help screen |
Other Useful Nmap Commands
| COMMAND | DESCRIPTION |
|---|---|
| nmap -iR 10 -PS22-25,80,113,1050,35000 -v -sn | Discovery only on ports x, no port scan |
| nmap 192.168.1.1-1/24 -PR -sn -vv | Arp discovery only on local network, no port scan |
| nmap -iR 10 -sn -traceroute | Traceroute to random targets, no port scan |
| nmap 192.168.1.1-50 -sL -dns-server 192.168.1.1 | Query the Internal DNS for hosts, list targets only |
| nmap 192.168.1.1 –packet-trace | Show the details of the packets that are sent and received during a scan and capture the traffic. |
