The command nmap -sX initiates what is known as a Xmas Scan. This type of scan is used to analyze how a target system responds to TCP packets with unusual flag combinations, helping the attacker identify live hosts and open ports without completing a full TCP handshake.

In the Xmas scan, three specific TCP flags are set in the packet:

URG (Urgent)

PSH (Push)

FIN (Finish)

This combination makes the packet appear "lit up like a Christmas tree," hence the name Xmas scan. These packets are sent to target ports to observe the system’s behavior, especially when it does not follow standard RFC 793 behavior.

Closed ports will usually respond with a RST (reset).

Open ports may not respond at all, depending on the operating system and configuration.

This method is typically used to evade detection by firewalls and intrusion detection systems that expect normal TCP traffic patterns.

Reference – CEH v13 Official Study Guide:

Module 03: Scanning Networks, Section: “TCP Scan Types”, Subsection: “Xmas Tree Scan”, Page Reference: typically listed under TCP Flag Scanning Techniques.

CEH v13 iLabs and practical guidance in CEH Engage also cover this scan in reconnaissance simulations.

Incorrect Options Explained:

A. SYN scan (-sS) sets only the SYN flag.

C. ACK scan (-sA) sets the ACK flag.

D. SYN and ACK flags are used in TCP handshake, not in Xmas scan.