This is my notes from the Junior Pentesting course at TryHackMe. This course takes you through the basics and some advanced topics regarding penetration testing.
Remember to add -sn if you are only interested in host discovery without port-scanning. Omitting -sn will let Nmap default to port-scanning the live hosts.
Option
Purpose
-n
no DNS lookup
-R
reverse-DNS lookup for all hosts
-sn
host discovery only
NMAP Basic Port Scans
Open: indicates that a service is listening on the specified port.
Closed: indicates that no service is listening on the specified port, although the port is accessible. By accessible, we mean that it is reachable and is not blocked by a firewall or other security appliances/programs.
Filtered: means that Nmap cannot determine if the port is open or closed because the port is not accessible. This state is usually due to a firewall preventing Nmap from reaching that port. Nmap’s packets may be blocked from reaching the port; alternatively, the responses are blocked from reaching Nmap’s host.
Unfiltered: means that Nmap cannot determine if the port is open or closed, although the port is accessible. This state is encountered when using an ACK scan -sA.
Open|Filtered: This means that Nmap cannot determine whether the port is open or filtered.
Closed|Filtered: This means that Nmap cannot decide whether a port is closed or filtered.
TCP Flags
URG: Urgent flag indicates that the urgent pointer filed is significant. The urgent pointer indicates that the incoming data is urgent, and that a TCP segment with the URG flag set is processed immediately without consideration of having to wait on previously sent TCP segments.
ACK: Acknowledgement flag indicates that the acknowledgement number is significant. It is used to acknowledge the receipt of a TCP segment.
PSH: Push flag asking TCP to pass the data to the application promptly.
RST: Reset flag is used to reset the connection. Another device, such as a firewall, might send it to tear a TCP connection. This flag is also used when data is sent to a host and there is no service on the receiving end to answer.
SYN: Synchronize flag is used to initiate a TCP 3-way handshake and synchronize sequence numbers with the other host. The sequence number should be set randomly during TCP connection establishment.
FIN: The sender has no more data to send.
Timings
Timings
Description
T0
paranoid (0)
T1
sneaky (1)
T2
polite (2)
T3
normal (3)
T4
aggressive (4)
T5
insane (5)
Summary
Port Scan Type
Example Command
TCP Connect Scan
nmap -sT MACHINE_IP
TCP SYN Scan
sudo nmap -sS MACHINE_IP
UDP Scan
sudo nmap -sU MACHINE_IP
These scan types should get you started discovering running TCP and UDP services on a target host.
These scan types rely on setting TCP flags in unexpected ways to prompt ports for a reply. Null, FIN, and Xmas scan provoke a response from closed ports, while Maimon, ACK, and Window scans provoke a response from open and closed ports.
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