312-50V10 · Question #630
Which Type of scan sends a packets with no flags set? Select the Answer
The correct answer is B. Null Scan. A Null Scan is a TCP port scanning technique that sends packets with all TCP flags cleared, making it stealthy and useful for evading some firewalls.
Question
Which Type of scan sends a packets with no flags set? Select the Answer
Options
- AOpen Scan
- BNull Scan
- CXmas Scan
- DHalf-Open Scan
How the community answered
(31 responses)- A3% (1)
- B87% (27)
- C3% (1)
- D6% (2)
Why each option
A Null Scan is a TCP port scanning technique that sends packets with all TCP flags cleared, making it stealthy and useful for evading some firewalls.
An Open Scan (TCP Connect scan) completes the full three-way handshake using SYN, SYN-ACK, and ACK flags, not packets with no flags.
A Null Scan sends TCP packets with no flags set (no SYN, FIN, RST, ACK, URG, or PSH bits). On open ports, RFC 793 compliant systems do not respond; on closed ports, a RST/ACK is returned, allowing port state inference while potentially bypassing stateless packet filters.
An Xmas Scan sets the FIN, URG, and PSH flags simultaneously, named for the packet lighting up like a Christmas tree, which is the opposite of a Null Scan.
A Half-Open (SYN) Scan sends a SYN packet and tears down the connection with a RST after receiving a SYN-ACK, so it does use TCP flags.
Concept tested: TCP Null Scan port scanning technique
Source: https://nmap.org/book/man-port-scanning-techniques.html
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