Which flag is not used in TCP SYN scanning?

In the context of TCP SYN scanning, the key focus is on identifying open ports on a target system by sending specially crafted TCP packets to analyze the responses received. TCP SYN scanning primarily involves the use of the SYN flag to initiate a connection request, and it relies heavily on how the target responds.

The SYN flag is utilized to signal a request to establish a connection. If the targeted port is open, the system will respond with a SYN-ACK, indicating it's ready to establish a session. Conversely, if the port is closed, the target will respond with a RST (reset). The ACK flag may be used in more nuanced scans, but for the primary activity of establishing a connection with SYN packets, its role is minimal compared to SYN.

The FIN flag, which indicates that the sender has finished sending data and wants to terminate the connection, is also not directly involved in the SYN scanning process. Instead, it may play a role in other scan types, such as FIN scanning. Similarly, the URG flag, which indicates that the packet contains urgent data, is unrelated to the initial SYN scanning technique.

Given this context, the FIN flag is the correct answer, as it is not used for probing the state of ports during a SYN scan