TryHackMe: Nmap Walkthrough

Nmap Logo at TryHackMe

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

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