TryHackMe: Nmap Walkthrough

This room teaches us about an in-depth look at scanning with Nmap, a powerful network scanning tool.

Task 1: Deploy

1. Deploy the attached VM. Answer: No answer needed.

Task 2: Introduction

1. What networking constructs are used to direct traffic to the right application on a server? Answer: Ports
2. How many of these are available on any network-enabled computer? Answer: 65535
3. [Research] How many of these are considered “well-known”? (These are the “standard” numbers mentioned in the task). Answer: 1024

Task 3: Nmap Switches

1. What is the first switch listed in the help menu for a ‘Syn Scan’ (more on this later!)? Answer: -sS
2. Which switch would you use for a “UDP scan”? Answer: -sU
3. If you wanted to detect which operating system the target is running on, which switch would you use? Answer: -O
4. Nmap provides a switch to detect the version of the services running on the target. What is this switch? Answer: -sV
5. The default output provided by nmap often does not provide enough information for a pentester. How would you increase the verbosity? Answer: -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). Answer: -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? Answer: -oA
8. What switch would you use to save the nmap results in a “normal” format? Answer: -oN
9. A very useful output format: how would you save results in a “grepable” format? Answer: -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 traceroute and common script scanning. How would you activate this setting? Answer: -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? Answer: -T5
12. We can also choose which port(s) to scan. How would you tell nmap to only scan port 80? Answer: -p 80
13. How would you tell nmap to scan ports 1000–1500? Answer: -p 1000–1500
14. A very useful option that should not be ignored: How would you tell nmap to scan all ports? Answer: -p-
15. How would you activate a script from the nmap scripting library (lots more on this later!)? Answer: — script
16. How would you activate all of the scripts in the “vuln” category? Answer: — script=vuln

Task 4: Scan Types Overview

1. Read the Scan Types Introduction. Answer: No answer needed

Task 5: Scan Types TCP Connect Scans

1. Which RFC defines the appropriate behaviour for the TCP protocol? Answer: RFC 793
2. If a port is closed, which flag should the server send back to indicate this? Answer: RST

Task 6: Scan Types SYN Scans

1. There are two other names for a SYN scan, what are they? Answer: Half-Open, Stealth
2. Can Nmap use a SYN scan without Sudo permissions (Y/N)? Answer: N

Task 7: Scan Types UDP Scans

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

Task 8: Scan Types NULL, FIN and Xmas

1. Which of the three shown scan types uses the URG flag? Answer: xmas
2. Why are NULL, FIN and Xmas scans generally used? Answer: Firewall Evasion
3. Which common OS may respond to a NULL, FIN or Xmas scan with a RST for every port? Answer: Microsoft Windows

Task 9: Scan Types 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). Answer: nmap -sn 172.16.0.0/16

Task 10: NSE Scripts Overview

1. What language are NSE scripts written in? Answer: Lua
2. Which category of scripts would be a very bad idea to run in a production environment? Answer: intrusive

Task 11: NSE Scripts Working with the NSE

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

Task 12: NSE Scripts 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? Answer: smb-os-discovery.nse
2. Read through this script. What does it depend on? Answer: smb-brute

Task 13: Firewall Evasion

1. Which simple (and frequently relied upon) protocol is often blocked, requiring the use of the -Pn switch? Answer: ICMP
2. [Research] Which Nmap switch allows you to append an arbitrary length of random data to the end of packets? Answer: — data-length

Task 14: Practical

1. Does the target (MACHINE_IP)respond to ICMP (ping) requests (Y/N)? Answer: N
2. Perform an Xmas scan on the first 999 ports of the target — how many ports are shown to be open or filtered? Answer: 999
3. There is a reason given for this — what is it? Note: The answer will be in your scan results. Think carefully about which switches to use — and read the hint before asking for help. Answer: No Response
4. Perform a TCP SYN scan on the first 5000 ports of the target — how many ports are shown to be open? Answer: 5
5. Open Wireshark (see Cryillic’s Wireshark Room for instructions) and perform a TCP Connect scan against port 80 on the target, monitoring the results. Make sure you understand what’s going on. Answer: No answer needed
6. Deploy the ftp-anon script against the box. Can Nmap login successfully to the FTP server on port 21? (Y/N). Answer: N

Task 15: Conclusion

1. Read the conclusion. Answer: No answer needed