Nmap

Date : 5th November, 2021

Author : Dhaval Kotak

Room : Nmap

Introduction

• Nmap can be used to perform many different kinds of port scan

• It can be used to scan for vulnerabilities, and in some cases even perform the exploit directly

• Depending on how the port responds, it can be determined as being open, closed, or filtered

1. What networking constructs are used to direct traffic to the right application on a server?

   Ports

2. How many of these are available on any network-enabled computer?

   65535

3. How many of these are considered "well-known"? (These are the "standard" numbers mentioned in the task)

   1024

Nmap Switches

1. What is the first switch listed in the help menu for a 'Syn Scan' (more on this later!)?

   -sS

2. Which switch would you use for a "UDP scan"?

   -sU

3. If you wanted to detect which operating system the target is running on, which switch would you use?

   -O

4. Nmap provides a switch to detect the version of the services running on the target. What is this switch?

   -sV

5. The default output provided by nmap often does not provide enough information for a pentester. How would you increase the verbosity?

   -v

6. Verbosity level one is good, but verbosity level two is better! How would you set the verbosity level to two? (Note: it's highly advisable to always use at least this option)

   -vv

7. We should always save the output of our scans -- this means that we only need to run the scan once (reducing network traffic and thus chance of detection), and gives us a reference to use when writing reports for clients.

   What switch would you use to save the nmap results in three major formats?

   -oA

8. What switch would you use to save the nmap results in a "normal" format?

   -oN

9. A very useful output format: how would you save results in a "grepable" format?

   -oG

10. Sometimes the results we're getting just aren't enough. If we don't care about how loud we are, we can enable "aggressive" mode. This is a shorthand switch that activates service detection, operating system detection, a trace route and common script scanning.

    How would you activate this setting?

    -A

11. Nmap offers five levels of "timing" template. These are essentially used to increase the speed your scan runs at. Be careful though: higher speeds are noisier, and can incur errors!

    How would you set the timing template to level 5?

    -T5

12. We can also choose which port(s) to scan.

    How would you tell nmap to only scan port 80?

    -p 80

13. How would you tell nmap to scan ports 1000-1500?

    -p 1000-1500

14. A very useful option that should not be ignored:

    How would you tell nmap to scan all ports?

    -p-

15. How would you activate a script from the nmap scripting library (lots more on this later!)?

    --script

16. How would you activate all of the scripts in the "vuln" category?

    --script=vuln

Scan Types

Overview

When port scanning with Nmap, there are three basic scan types. These are:

• TCP Connect Scans (-sT)

• SYN "Half-open" Scans (-sS)

• UDP Scans (-sU)

Additionally there are several less common port scan types, some of which we will also cover (albeit in less detail). These are:

• TCP Null Scans (-sN)

• TCP FIN Scans (-sF)

• TCP Xmas Scans (-sX)

Most of these (with the exception of UDP scans) are used for very similar purposes, however, the way that they work differs between each scan. This means that, whilst one of the first three scans are likely to be your go-to in most situations, it's worth bearing in mind that other scan types exist.

TCP Scans

1. Which RFC defines the appropriate behaviour for the TCP protocol?

   RFC 793

2. If a port is closed, which flag should the server send back to indicate this?

   RST

SYN Scans

1. There are two other names for a SYN scan, what are they?

   Half-Open, Stealth

2. Can Nmap use a SYN scan without Sudo permissions (Y/N)?

   N

UDP Scans

1. If a UDP port doesn't respond to an Nmap scan, what will it be marked as?

   open|filtered

2. When a UDP port is closed, by convention the target should send back a "port unreachable" message. Which protocol would it use to do so?

   ICMP

Null, FIN and Xmas

1. Which of the three shown scan types uses the URG flag?

   xmas

2. Why are NULL, FIN and Xmas scans generally used?

   firewall evasion

3. Which common OS may respond to a NULL, FIN or Xmas scan with a RST for every port?

   Microsoft Windows

ICMP Network Scanning

1. How would you perform a ping sweep on the 172.16.x.x network (Netmask: 255.255.0.0) using Nmap? (CIDR notation)

   nmap -sn 172.16.0.0/16

NSE Scripts

Overview

The Nmap Scripting Engine (NSE) is an incredibly powerful addition to Nmap, extending its functionality quite considerably. NSE Scripts are written in the Lua programming language, and can be used to do a variety of things: from scanning for vulnerabilities, to automating exploits for them. The NSE is particularly useful for reconnaissance, however, it is well worth bearing in mind how extensive the script library is.

1. What language are NSE scripts written in?

   Lua

2. Which category of scripts would be a very bad idea to run in a production environment? intrusive

Working with the NSE

1. What optional argument can the ftp-anon.nse script take?

   maxlist

Searching for Scripts

1. Search for "smb" scripts in the /usr/share/nmap/scripts/ directory using either of the demonstrated methods. What is the filename of the script which determines the underlying OS of the SMB server?

   smb-os-discovery.nse

2. Read through this script. What does it depend on?

   smb-brute

Firewall Evasion

1. Which simple (and frequently relied upon) protocol is often blocked, requiring the use of the -Pn switch?

   ICMP

2. Which Nmap switch allows you to append an arbitrary length of random data to the end of packets?

   --data-length

Practical

1. Does the target (MACHINE_IP)respond to ICMP (ping) requests (Y/N)?

   N

2. Perform an Xmas scan on the first 999 ports of the target -- how many ports are shown to be open or filtered?

   999

3. There is a reason given for this -- what is it?

   No response

4. Perform a TCP SYN scan on the first 5000 ports of the target -- how many ports are shown to be open?

   5

5. Deploy the ftp-anon script against the box. Can Nmap login successfully to the FTP server on port 21? (Y/N)

   Y