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Nmap

Notes

  • Passing an ip is better than using domain name

    • else nmap will spend time doing a reverse domain lookup

    • but an ip can also have multiple domain under it

      • which could be used to attack it

  • if you know target is online pass the flag for telling it not to do a ping

    • Pass the -Pn flag

  • Nmap used the response of port scan as well as the network header to determine the OS

    • this is a probability

    • this can be increased by various NSE scripts

  • Suggestion

    • Always save it to a file

  • the order of the flags are also important if you do a -sv and the a -p- it will do a banner grab on every port

    • instead if you do a -p- first then a first check if the port is open and then does a banner grab

    • https://youtu.be/Sz2y34lE_Z0?t=1978

Nmap Commands

Basic

nmap -Pn -n -A -vvv -oN nmap/00-basic.txt -iL target.txt

TCP port scan Full

nmap -n -p- -vvv -oN nmap/01-full-port-scan.txt -iL target.txt

UDP port scan Full

sudo nmap -vvv -sU -n -p- -oN nmap/02-udp-full-port-scan.txt -iL target.txt

Top 1000 UDP port scan Full

sudo nmap -vvv -sU -n -p- -oN nmap/02.5-udp-top-1000-port-scan.txt -iL target.txt

Detail scan

sudo nmap -vvv -sC -A -O -osscan-guess -sV -version-all -oN nmap/03-detail-scan.txt -iL target.txt -p <port number T:80 t is tcp>

Convert nmap xml to html

 xsltproc target.xml -o target.html

Type of Scans

-sT

  • most stealthy where the whole connection is made

    • most stealthy since many firewalls are tuned to look for half open connections

    • SYN > SYN/ ACK > ACK

  • also the most accurate

  • but takes the most time

-sA

  • only sends a ACK packet

  • done to understand the firewall rule set

  • works if firewall is stateless

  • https://explainshell.com/explain?cmd=nmap+-sA

-sS

  • default scan of nmap

  • Sends only a SYN packet

  • can be detected by firewalls after potential 2 packet , 3 to prove a trend

  • also the fastest scan

-sU

  • performs UDP scan

  • still does a ping first

  • Don't know why Nmap tries to connect on port 80 with TCP in a UDP scan

-Pn

  • nmap always does a icmp request to check if the port is up

  • this tell nmap not to do a ping request

-sV

  • discovers service version by banner grabbing

-O

  • discovers OS details from ports and TTL

-A

  • does os discovers (-O) and service discovery along with their versions

Cheat sheet

Nmap Option

Description

10.10.10.0/24

Target network range.

-sn

Disables port scanning.

-Pn

Disables ICMP Echo Requests

-n

Disables DNS Resolution.

-PE

Performs the ping scan by using ICMP Echo Requests against the target.

--packet-trace

Shows all packets sent and received.

--reason

Displays the reason for a specific result.

--disable-arp-ping

Disables ARP Ping Requests.

--top-ports=<num>

Scans the specified top ports that have been defined as most frequent.

-p-

Scan all ports.

-p22-110

Scan all ports between 22 and 110.

-p22,25

Scans only the specified ports 22 and 25.

-F

Scans top 100 ports.

-sS

Performs an TCP SYN-Scan.

-sA

Performs an TCP ACK-Scan.

-sU

Performs an UDP Scan.

-sV

Scans the discovered services for their versions.

-sC

Perform a Script Scan with scripts that are categorized as "default".

--script <script>

Performs a Script Scan by using the specified scripts.

-O

Performs an OS Detection Scan to determine the OS of the target.

-A

Performs OS Detection, Service Detection, and traceroute scans.

-D RND:5

Sets the number of random Decoys that will be used to scan the target.

-e

Specifies the network interface that is used for the scan.

-S 10.10.10.200

Specifies the source IP address for the scan.

-g

Specifies the source port for the scan.

--dns-server <ns>

DNS resolution is performed by using a specified name server.

Output Options

Nmap Option

Description

-oA filename

Stores the results in all available formats starting with the name of "filename".

-oN filename

Stores the results in normal format with the name "filename".

-oG filename

Stores the results in "grepable" format with the name of "filename".

-oX filename

Stores the results in XML format with the name of "filename".

Performance Options

Nmap Option

Description

--max-retries <num>

Sets the number of retries for scans of specific ports.

--stats-every=5s

Displays scan's status every 5 seconds.

-v/-vv

Displays verbose output during the scan.

--initial-rtt-timeout 50ms

Sets the specified time value as initial RTT timeout.

--max-rtt-timeout 100ms

Sets the specified time value as maximum RTT timeout.

--min-rate 300

Sets the number of packets that will be sent simultaneously.

-T <0-5>

Specifies the specific timing template.

Types of Port States

State

Description

open

This indicates that the connection to the scanned port has been established. These connections can be TCP connections, UDP datagrams as well as SCTP associations.

closed

When the port is shown as closed, the TCP protocol indicates that the packet we received back contains an RST flag. This scanning method can also be used to determine if our target is alive or not.

filtered

Nmap cannot correctly identify whether the scanned port is open or closed because either no response is returned from the target for the port or we get an error code from the target.

unfiltered

This state of a port only occurs during the TCP-ACK scan and means that the port is accessible, but it cannot be determined whether it is open or closed.

open|filtered

If we do not get a response for a specific port, Nmap will set it to that state. This indicates that a firewall or packet filter may protect the port.

closed|filtered

This state only occurs in the IP ID idle scans and indicates that it was impossible to determine if the scanned port is closed or filtered by a firewall.

Firewall and IDS/IPS Evasion

  • think about the kind of [[Firewalls]] that would be in place

Determine Firewalls and Their Rules

  • This is different for rejected packets that are returned with an RST flag. These packets contain different types of ICMP error codes or contain nothing at all.

    • Such errors can be:

      • Net Unreachable

      • Net Prohibited

      • Host Unreachable

      • Host Prohibited

      • Port Unreachable

      • Proto Unreachable

  • Nmap's TCP ACK scan (-sA) method is much harder to filter for firewalls and IDS/IPS systems than regular SYN (-sS) or Connect scans (-sT)

    • because they only send a TCP packet with only the ACK flag

    • When a port is closed or open, the host must respond with an RST flag.

    • Unlike outgoing connections, all connection attempts (with the SYN flag) from external networks are usually blocked by firewalls.

    • However, the packets with the ACK flag are often passed by the firewall because the firewall cannot determine whether the connection was first established from the external network or the internal network.

    • works if the firewall is stateless

Detect IDS/IPS

  • Several virtual private servers (VPS) with different IP addresses are recommended to determine whether such systems are on the target network during a penetration test

Scan by Using Decoys

sudo nmap 10.129.2.28 -p 80 -sS -Pn -n --disable-arp-ping --packet-trace -D RND:5

Scanning Options

Description

10.129.2.28

Scans the specified target.

-p 80

Scans only the specified ports.

-sS

Performs SYN scan on specified ports.

-Pn

Disables ICMP Echo requests.

-n

Disables DNS resolution.

--disable-arp-ping

Disables ARP ping.

--packet-trace

Shows all packets sent and received.

-D RND:5

Generates five random IP addresses that indicates the source IP the connection comes from.

SYN-Scan From DNS Port

sudo nmap 10.129.2.28 -p50000 -sS -Pn -n --disable-arp-ping --packet-trace --source-port 53

Nmap Scripting Engine

Category

Description

auth

Determination of authentication credentials.

broadcast

Scripts, which are used for host discovery by broadcasting and the discovered hosts, can be automatically added to the remaining scans.

brute

Executes scripts that try to log in to the respective service by brute-forcing with credentials.

default

Default scripts executed by using the -sC option.

discovery

Evaluation of accessible services.

dos

These scripts are used to check services for denial of service vulnerabilities and are used less as it harms the services.

exploit

This category of scripts tries to exploit known vulnerabilities for the scanned port.

external

Scripts that use external services for further processing.

fuzzer

This uses scripts to identify vulnerabilities and unexpected packet handling by sending different fields, which can take much time.

intrusive

Intrusive scripts that could negatively affect the target system.

malware

Checks if some malware infects the target system.

safe

Defensive scripts that do not perform intrusive and destructive access.

version

Extension for service detection.

vuln

Identification of specific vulnerabiliti

Specific Scripts Category

Nmap Scripting Engine

groot@htb[/htb]$ sudo nmap <target> --script <category>

Defined Scripts

Nmap Scripting Engine

cyberaestheticgroot@htb[/htb]$ sudo nmap <target> --script <script-name>,<script-name>,...

Nmap - Aggressive Scan

sudo nmap 10.129.2.28 -p 80 -A

  • only runs the default scripts not all scripts

Reference

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