A penetration tester wants to inventory live TCP services on a DMZ host while minimizing the chance that the host application logs the activity. Using the standard Nmap syntax, which scan type meets this goal by sending only an initial SYN and interpreting the target's SYN-ACK or RST response instead of completing the three-way handshake?
The TCP SYN (half-open) scan, invoked in Nmap with the -sS option, transmits a single SYN packet to each port. If the target replies with SYN-ACK the port is marked open; if it replies with RST the port is closed. Because the tester immediately resets the connection instead of sending the final ACK, no full TCP session is established, so most applications never record the attempt. TCP connect scan (-sT) completes the handshake and is more easily logged, while ACK (-sA) and FIN (-sF) scans are used primarily for firewall rule discovery and stealth probing of stateless filters, not for reliable open-port enumeration on modern systems.
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Why is a TCP SYN (half-open) scan considered stealthy?
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What differentiates TCP connect scans from TCP SYN scans?
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What are TCP FIN and ACK scans used for in penetration testing?
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Why is the TCP SYN (half-open) scan less likely to be logged by the host application?
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What is the purpose of the three-way TCP handshake, and why doesn't the SYN scan use it?
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How does the TCP SYN scan (-sS) differ from other scan types like FIN (-sF) or ACK (-sA)?
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Reconnaissance Techniques
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