What keeps a packet sent during Xmas scanning "lit up like a Christmas tree"?

The concept of "Xmas scanning" derives its name from the way packets are sent with multiple flags set, which can make the packet appear "lit up like a Christmas tree." In this type of scan, various flags in the TCP header are manipulated to probe the responsiveness of networked devices. The use of the FIN, PSH, and URG flags in a single packet is what characterizes an Xmas scan.

Each of these flags serves a specific purpose in the TCP protocol:

• The FIN flag signifies that the sender has finished sending data.

• The PSH flag indicates that the sender is requesting the receiver to process the packet immediately.

• The URG flag indicates that the data contained within this segment is urgent and should be prioritized.

When all these flags are set in a single packet, it creates a unique signature that can elicit varied responses from devices, allowing an attacker to map the network and identify open or closed ports based on the responses received. This is why the correct answer emphasizes that setting multiple flags is critical to this scanning technique.