The following Nmap cheat sheet aims to explain what Nmap is, what it does, and how to use it by providing Nmap command examples in a cheat sheet style documentation format.

Orignal Published Date: 11th December 2014

What is Nmap?

Nmap (network mapper), the god of port scanners used for network discovery and the basis for most security enumeration during the initial stages of a penetration test. The tool was written and maintained by Fyodor AKA Gordon Lyon.

Nmap displays exposed services on a target machine along with other useful information such as the verion and OS detection.

Nmap has made twelve movie appearances, including The Matrix Reloaded, Die Hard 4, Girl With the Dragon Tattoo, and The Bourne Ultimatum.

Nmap Trinity

What does Nmap do:

  • Host discovery
  • Port discovery / enumeration
  • Service discovery
  • Operating system version detection
  • Hardware (MAC) address detection
  • Service version detection
  • Vulnerability / exploit detection, using Nmap scripts (NSE)
  • Nmap IDS / Portscan Detection & Scan Time Optimisation

Download & Install Nmap

Nmap can be downloaded from nmap.org, however commonly Nmap is installed via your Linux distributions package manager:

Debian / Ubuntu / Kali

How to Install Nmap on Ubuntu, Debian, Kali or other Linux systems using the APT package manager.

apt install nmap

Nmap RHEL / Fedora

How to Install Nmap on RHEL, Fedora, CentOS, Rocky Linux or other Linux systems using the DNF package manager.

dnf install nmap

Nmap Windows

Download Nmap for Windows and install: Nmap for Windows

Nmap MacOS

How to install nmap on MacOS using Brew.

brew install nmap

Nmap Commands

Basic Nmap scanning command examples, often used at the first stage of enumeration.

Command Description

nmap -sP 10.0.0.0/24

Nmap scan the network, listing machines that respond to ping.

nmap -p 1-65535 -sV -sS -T4 target

A full TCP port scan using with service version detection - T1-T5 is the speed of the scan.

nmap -v -sS -A -T4 target

Prints verbose output, runs stealth syn scan, T4 timing, OS and version detection + traceroute and scripts against target services.

nmap -v -sS -A -T5 target

Prints verbose output, runs stealth syn scan, T5 timing, OS and version detection + traceroute and scripts against target services.

nmap -v -sV -O -sS -T5 target

Prints verbose output, runs stealth syn scan, T5 timing, OS and version detection.

nmap -v -p 1-65535 -sV -O -sS -T4 target

Prints verbose output, runs stealth syn scan, T4 timing, OS and version detection + full port range scan.

nmap -v -p 1-65535 -sV -O -sS -T5 target

Prints verbose output, runs stealth syn scan, T5 timing, OS and version detection + full port range scan.
Agressive scan timings are faster, but could yeild inaccurate results!

T5 uses very aggressive scan timings and could lead to missed ports, T3-4 is a better compromise if you need fast results (depending on if local network or remote).

Nmap scan from file

Command Description

nmap -iL ip-addresses.txt

Scans a list of IP addresses, you can add options before / after.

Nmap Scan all Ports

Command Description

nmap -p- target

Nmap scan all ports, a full scan of all TCP ports on a target.

Nmap output formats

Command Description

nmap -sS -sV -T5 10.0.1.99 -oA output-all-formats

nmap output to all formats.

nmap -sV -p 139,445 -oG grep-output.txt 10.0.1.0/24

Outputs "grepable" output to a file, in this example Netbios servers.

E.g, The output file could be grepped for "Open".

nmap -sS -sV -T5 10.0.1.99 --webxml -oX -
| xsltproc --output file.html -

Export nmap output to HTML report.

Nmap Netbios Examples

Command Description

nmap -sV -v -p 139,445 10.0.0.1/24

Find all Netbios servers on subnet

nmap -sU --script nbstat.nse -p 137 target

Nmap display Netbios name

nmap --script-args=unsafe=1 --script
smb-check-vulns.nse -p 445 target

Nmap check if Netbios servers are vulnerable to MS08-067
--script-args=unsafe=1 has the potential to crash servers / services

Becareful when running this command.

Nmap Nikto Scan

Nmap + Nikto scanning for specific discovered HTTP ports.

Command Description

nmap -p80 10.0.1.0/24 -oG - | nikto.pl -h -

Scans for http servers on port 80 and pipes into Nikto for scanning.

nmap -p80,443 10.0.1.0/24 -oG - | nikto.pl -h -

Scans for http/https servers on port 80, 443 and pipes into Nikto for scanning.

Nmap Cheatsheet

Target Specification

Nmap allows hostnames, IP addresses, subnets.

Example:

blah.highon.coffee, nmap.org/24, 192.168.0.1; 10.0.0-255.1-254
Command Description

-iL

inputfilename: Input from list of hosts/networks

-iR

iterate hosts: Choose random targets from the input file

--exclude

host1[,host2][,host3],... : Exclude hosts/networks

--excludefile

exclude_file: nmap exclude hosts list from file

Host Discovery

Command Description

-sL

List Scan - simply list targets to scan

-sn

Nmap ping scan / sweep - runs a nmap network scan, with port scanning disabled

-Pn

Treat all hosts as online -- skip host discovery

-PS/PA/PU/PY[portlist]

TCP SYN/ACK, UDP or SCTP discovery to given ports. Allows you to specify a specific port nmap uses to verify a host is up e.g., -PS22 (by default nmap sends to a bunch of common ports, this allows you to be specific)

-PE/PP/PM

ICMP echo, timestamp, and netmask request discovery probes

-PO[protocol list]

IP Protocol Ping

-n/-R

Never do DNS resolution/Always resolve [default: sometimes]

Scan Techniques

Command Description

-sS
-sT
-sA
-sW
-sM

TCP SYN scan
Connect scan
ACK scan
Window scan
Maimon scan

-sU

UDP Scan

-sN
-sF
-sX

TCP Null scan
FIN scan
Xmas scan

--scanflags

Customize TCP scan flags

-sI zombie host[:probeport]

Idle scan

-sY
-sZ

SCTP INIT scan
COOKIE-ECHO scan

-sO

IP protocol scan

-b "FTP relay host"

FTP bounce scan

Port Specification and Scan Order

Command Description

-p

Specify ports, e.g. -p80,443 or -p1-65535

-p U:PORT

Scan UDP ports with Nmap, e.g. -p U:53

-F

Fast mode, scans fewer ports than the default scan

-r

Scan ports consecutively - don't randomize

--top-ports "number"

Scan "number" most common ports

--port-ratio "ratio"

Scan ports more common than "ratio"

Service Version Detection

Command Description

-sV

Probe open ports to determine service/version info

--version-intensity "level"

Set from 0 (light) to 9 (try all probes)

--version-light

Limit to most likely probes (intensity 2)

--version-all

Try every single probe (intensity 9)

--version-trace

Show detailed version scan activity (for debugging)

Script Scan

Command Description

-sC

equivalent to --script=default

--script="Lua scripts"

"Lua scripts" is a comma separated list of directories, script-files or script-categories

--script-args=n1=v1,[n2=v2,...]

provide arguments to scripts

-script-args-file=filename

provide NSE script args in a file

--script-trace

Show all data sent and received

--script-updatedb

Update script database

--script-help="Lua scripts"

Show help about scripts

OS Detection

Command Description

-O

Enable OS Detection

--osscan-limit

Limit OS detection to promising targets

--osscan-guess

Guess OS more aggressively

Timing and Performance

Options which take TIME are in seconds, or append 'ms' (milliseconds), 's' (seconds), 'm' (minutes), or 'h' (hours) to the value (e.g. 30m).

Command Description

-T 0-5

Set timing template - higher is faster (less accurate)

--min-hostgroup SIZE
--max-hostgroup SIZE

Parallel host scan group sizes

--min-parallelism NUMPROBES
--max-parallelism NUMPROBES

Probe parallelization

--min-rtt-timeout TIME
--max-rtt-timeout TIME
--initial-rtt-timeout TIME

Specifies probe round trip time

--max-retries TRIES

Caps number of port scan probe retransmissions

--host-timeout TIME

Give up on target after this long

--scan-delay TIME
--max-scan-delay TIME

Adjust delay between probes

--min-rate NUMBER

Send packets no slower than NUMBER per second

--max-rate NUMBER

Send packets no faster than NUMBER per second

Firewalls IDS Evasion and Spoofing

Command Description

-f; --mtu VALUE

Fragment packets (optionally w/given MTU)

-D decoy1,decoy2,ME

Cloak a scan with decoys

-S IP-ADDRESS

Spoof source address

-e IFACE

Use specified interface

-g PORTNUM
--source-port PORTNUM

Use given port number

--proxies url1,[url2],...

Relay connections through HTTP / SOCKS4 proxies

--data-length NUM

Append random data to sent packets

--ip-options OPTIONS

Send packets with specified ip options

--ttl VALUE

Set IP time to live field

--spoof-mac ADDR/PREFIX/VENDOR

Spoof Nmap MAC address

--badsum

Send packets with a bogus TCP/UDP/SCTP checksum

Nmap Scan Output File Options

Command Description

-oN

Output Normal

-oX

Output to XML

-oS

Script Kiddie / 1337 speak... sigh

-oG

Output greppable - easy to grep nmap output

-oA BASENAME

Output in the three major formats at once

-v

Increase verbosity level use -vv or more for greater effect

-d

Increase debugging level use -dd or more for greater effect

--reason

Display the reason a port is in a particular state

--open

Only show open or possibly open ports

--packet-trace

Show all packets sent / received

--iflist

Print host interfaces and routes for debugging

--log-errors

Log errors/warnings to the normal-format output file

--append-output

Append to rather than clobber specified output files

--resume FILENAME

Resume an aborted scan

--stylesheet PATH/URL

XSL stylesheet to transform XML output to HTML

--webxml

Reference stylesheet from Nmap.Org for more portable XML

--no-stylesheet

Prevent associating of XSL stylesheet w/XML output

Misc Nmap Options

Command Description

-6

Enable IPv6 scanning

-A

Enable OS detection, version detection, script scanning, and traceroute

--datedir DIRNAME

Specify custom Nmap data file location

--send-eth
--send-ip

Send using raw ethernet frames or IP packets

--privileged

Assume that the user is fully privileged

--unprivileged

Assume the user lacks raw socket privileges

-V

Show nmap version number

-h

Show nmap help screen

Nmap Enumeration Command Examples

The following are real world examples of Nmap enumeration.

Enumerating Netbios

The following example enumerates Netbios on the target networks, the same process can be applied to other services by modifying ports / NSE scripts.

Detect all exposed Netbios servers on the subnet.

Nmap find exposed Netbios servers

root:~# nmap -sV -v -p 139,445 10.0.1.0/24


Starting Nmap 6.47 ( http://nmap.org ) at 2014-12-11 21:26 GMT
 Nmap scan report for nas.decepticons 10.0.1.12
 Host is up (0.014s latency).
PORT STATE SERVICE VERSION
 139/tcp open netbios-ssn Samba smbd 3.X (workgroup: MEGATRON)
 445/tcp open netbios-ssn Samba smbd 3.X (workgroup: MEGATRON)
Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 256 IP addresses (1 hosts up) scanned in 28.74 seconds
 </p>

Nmap find Netbios name.

Nmap find exposed Netbios servers

root:~# nmap -sU --script nbstat.nse -p 137 10.0.1.12


Starting Nmap 6.47 ( http://nmap.org ) at 2014-12-11 21:26 GMT
 Nmap scan report for nas.decepticons 10.0.1.12
 Host is up (0.014s latency).
PORT STATE SERVICE VERSION
 137/udp open netbios-ns
Host script results:
 |_nbstat: NetBIOS name: STARSCREAM, NetBIOS user: unknown, NetBIOS MAC: unknown (unknown)
Nmap done: 256 IP addresses (1 hosts up) scanned in 28.74 seconds
 </p>

Nmap Netbios MS08-067

How to scan a target and identify if it is vulnerable to MS08-067

Nmap check MS08-067

root:~# nmap --script-args=unsafe=1 --script smb-check-vulns.nse -p 445 10.0.0.1


Nmap scan report for ie6winxp.decepticons (10.0.1.1)
 Host is up (0.00026s latency).
 PORT STATE SERVICE
 445/tcp open microsoft-ds
 Host script results:
 | smb-check-vulns:
 | MS08-067: VULNERABLE
 | Conficker: Likely CLEAN
 | regsvc DoS: NOT VULNERABLE
 | SMBv2 DoS (CVE-2009-3103): NOT VULNERABLE
 |_ MS07-029: NO SERVICE (the Dns Server RPC service is inactive)
 Nmap done: 1 IP address (1 host up) scanned in 5.45 seconds
 </p>

The information gathered during the enumeration indicates the target is vulnerable to MS08-067, exploitation will confirm if it’s vulnerable to MS08-067.

Nmap Scan Tuning & Optimisation

Nmap Rate

To speed up your scan increase the rate, be aware that setting a high rate value will result in a less accurate scan.

--max-rate 
--min-rate

Nmap Parallelism

The maximum or minimum amount of parallel tasks scanned at the same time (in parallel).

TIP: If you have an basic IDS / portscan detection blocking your scans you could lower the –min-parallelism in an attempt to reduce the number of concurrent connections

--min-parallelism
--max-parallelism

Nmap Host Group Sizes

The number of hosts scanned at the same time, Note: if you are writing output to a file e.g., -oA you will need to wait for the host group to complete scanning before the nmap output will be written to the file. Therefore if you get a lagging host you will may end up waiting a while for the output file, which brings us on to… host timeout.

--min-hostgroup 
--max-hostgroup

Nmap Host Timeout

Nmap allows you to specify the timeout, which is the length of time it waits before giving up on the target. Be careful setting this super low, as you may end up with inaccurate results.

The following example would giveup after 50 seconds.

--host-timeout 50

Nmap Scan Delay

An extremely useful option to defeat basic port scan detection (SOHO devices and some IDS) that essentially monitor and block X amount of connects per second (syn flood etc). In short the scan timing can be optimised to allow nmap to bypass firewall detection mechanism.

--scan-delay 5s

For example if you know you can get away with 2 req/sec without getting blacklisted then you could use:

--scan-delay 1.2

added 200ms for a buffer

Nmap Disable DNS Lookups

Assuming you do not want domain names being looked up, use the -n flag to dissable resolution and speed up the scan.

Nmap Black List Detection?

  1. It ussally takes and extemely long time to complete
  2. Droppped probes nmap will increase the timeout, but it’s likely you are already black listed
  3. To confirm, recheck a port that you know was open before

As far as I know there is no way of detecting for black listing within nmap natively.

Nmap Optimising Portscans for Targets

Once you have identified a target firewall / IDS you can look up the default settings for the portscan black list by reading the manual and use the nmap command switches above to obtain the best performance without getting black listed.

If you found this Nmap cheat sheet useful, please share it below.

Nmap FAQ

What is Nmap Used for?

Nmap (Network Mapper) is a free and open source tool for discovering and auditing networks. Many system and network administrators use Nmap to perform network inventories, asset management , manage service updating schedules, and monitor host or service availability.

Is Nmap Illegal?

When used properly, Nmap could help you protect your network from intruders. But used inappropriately (e.g., maliciously, and/or without permission from the target), Nmap could (in rare cases) get you sued, fired, expelled, jailed, or banned by your ISP.

Is Nmap a Vulnerability Scanner

Nmap is a port scanner or network mapper, the tool identified if a system exists on the network or IP address you provide. However, NSE Scripts then extend the functionality of Nmap by allowing additional host checkes that provide nmap vulnerability scanning functionality to the tool.

Why do hackers use Nmap?

Attackers or hackers may use Nmap to identify targets and the exposed ports on a target in an effort to idenitfy potential attack surface to perform addtional security testing against.

Nmap Download

You can download nmap from https://nmap.org/download or a common option would be to install via your Linux distributions package manager or Brew on macos.

Nmap Scripts List

You can find a lot of the current Nmap scripts list at https://nmap.org/nsedoc/scripts/ this list is actively updated by the Nmap project.

Document Changelog

  • Original Post Date: 13/12/2014
  • Last Updated: 10/06/2024 (10th of June 2024)
  • Author: Arr0way
  • Notes: Checked syntax was current for latest version of Nmap + added additional content.