Which scan type is a variant of inverse TCP scanning that uses the FIN, URG, and PUSH flags set to send a TCP frame to a remote device?

• A. Xmas Scan
• B. Inverse TCP Flag Scan
• C. ACK Flag Probe Scan
• D. TTL-Based ACK Flag Probing Scanning

Answer: (A)

This question is about recognizing a TCP scan technique by the flags it uses. The key idea is that different flag combinations in a TCP header create distinct scan methods, each with its own behavior and purpose for probing ports.

The Xmas scan sets FIN, URG, and PUSH (PSH) flags all at once in a single TCP segment. This combination gives the packet a “lit Christmas tree” appearance, which is where the name comes from. It’s considered a variant of FIN-based scans that aim to be stealthier, by sending unusual-looking packets that may bypass some simple firewalls or detection rules. How the target responds (or doesn’t respond) helps infer whether a port is open or closed: typically, a closed port replies with a reset, while an open port often yields no response. This pattern is exactly what the described method is designed to do—send a TCP frame with those specific flags to a remote device in order to probe port status covertly.

Other options involve different flag usage or probing techniques that don’t match this FIN/URG/PSH flag combination, so they aren’t the same method.