Why Does an Nmap Xmas Scan Returning RST Mean All Ports Are Closed?

During a vulnerability scan a penetration tester enters the following Nmap command against all of the non-Windows clients: nmap –sX –T4 –p 21-25, 67, 80, 139, 8080 192.168.11.191 The penetration tester reviews the packet capture in Wireshark and notices that the target responds with an RST packet flag set for all of the targeted ports. Which of the following does this information most likely indicate?

All of the ports in the target range are closed. Source Reference Answer
Nmap needs more time to scan the ports in the target range.
The ports in the target range cannot be scanned because they are common UDP ports.
All of the ports in the target range are open.

Community Votes

100%

100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Community Insight

This question tests packet-capture interpretation of Nmap scan responses; the trap is mistaking any response for an open port, when an RST to a Xmas probe specifically signals a closed port.

Xmas scans (-sX) send TCP packets with FIN, PSH, and URG flags; per RFC 793, closed ports respond with RST. Community consensus confirms that when all targeted ports return RST, it indicates all the ports are closed.

Choosing D (all ports are open) is the most common mistake. Test takers may assume an active RST reply indicates the port is listening, but Xmas-scan behavior is the opposite: open ports remain silent, while closed ports reply with RST.

Community Discussion (3 comments)

Etc_Shadow28000 👍 1 Selected: A

The -sX option specifies a Xmas scan, which sends packets with the FIN, PSH, and URG flags set. The target’s response to such a scan provides information about the state of the ports. When the penetration tester reviews the packet capture in Wireshark and notices that the target responds with an RST (reset) packet for all of the targeted ports, this most likely indicates: A. All of the ports in the target range are closed. Explanation: B. The response received (RST packets) is definitive and indicates the state of the ports, so additional time would not change these results. C. The ports listed (21-25, 67, 80, 139, 8080) are primarily TCP ports (except for port 67 which is typically used for DHCP, a UDP service). However, the response being an RST indicates the scan was conducted over TCP. D. If the ports were open, the target would not send RST packets in response to a Xmas scan. Typically, open ports would simply ignore the Xmas scan packet (no response).

aee9303 👍 1

There are a few circumstances in which a TCP packet might not be expected; the two most common are: The packet is an initial SYN packet trying to establish a connection to a server port on which no process is listening. The packet arrives on a TCP connection that was previously established, but the local application already closed its socket or exited and the OS closed the socket. Other circumstances are possible, but are unlikely outside of malicious behavior such as attempts to hijack a TCP connection.

Big_Dre 👍 1 Selected: A

all targeted ports are close

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Expert Analysis

Why the Answer Is Correct

A Xmas scan (-sX) sends TCP packets with FIN, PSH, and URG flags set. According to RFC 793, a closed TCP port is expected to respond with an RST packet. The scenario states that the target returns an RST for every targeted port, which is the classic closed-port response. The top-voted community comment explains this exactly, noting that the -sX option specifies a Xmas scan and that the RST responses reveal the state of the ports.

Why the Other Options Are Wrong

Option B is wrong because an RST reply is a definitive response, not a sign that Nmap needs more time; timeouts or slow scans would produce no response, not RST packets. Option C is incorrect because the listed ports (21-25, 67, 80, 139, 8080) are TCP ports, not UDP, and -sX is a TCP-based scan. Option D is the opposite of the actual behavior; open ports in a Xmas scan generally do not respond, while closed ports send RST. A community comment about RST circumstances further reinforces that RST indicates no process is listening on the port.

Community Comment Notes

The most-liked comment identifies the correct choice immediately and explains the Xmas scan flag behavior. Another comment provides general TCP network knowledge, noting that RST packets often indicate a port with no listener, which aligns with answer A. A third comment simply agrees with A, and no comments support any alternative answer. Overall, the community firmly backs option A.

Official Reference

Exam Strategy

When you see a Nmap scan type in the question, immediately recall its response characteristics: Xmas (-sX) and FIN (-sF) scans provoke RST from closed ports and silence from open/filtered ones. On PT0-002, distinguish between scan-time responses and open-port indications, and read the packet-capture clue carefully before choosing an option.

Related Analysis

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