312-50V11 · 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 sends TCP packets with all flag bits set to zero, exploiting how RFC-compliant systems respond to flagless packets.
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
(50 responses)- A6% (3)
- B88% (44)
- C4% (2)
- D2% (1)
Why each option
A Null scan sends TCP packets with all flag bits set to zero, exploiting how RFC-compliant systems respond to flagless packets.
An 'Open Scan' is not a standard scan type; TCP connect scans complete the full three-way handshake using SYN, SYN-ACK, and ACK flags.
In a Null scan, the TCP packet header has no flags (SYN, ACK, FIN, RST, URG, PSH) set, resulting in a value of 0. RFC 793-compliant systems will respond with an RST for closed ports and give no response for open ports, allowing stealthy port enumeration without completing a connection.
A Xmas scan sets the FIN, URG, and PSH flags simultaneously, the opposite of a Null scan which sets no flags.
A Half-Open (SYN) scan sends packets with only the SYN flag set to initiate but never complete the TCP handshake.
Concept tested: TCP Null scan packet flags and behavior
Source: https://nmap.org/book/man-port-scanning-techniques.html
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