The answer is the -sV flag, which is the correct choice because it enables Nmap service version detection by sending probe packets to open ports and analyzing the responses to identify the exact application and version running on the listening port. In a reverse shell scenario, the command-and-control server’s listening port could be running a custom listener, SSH, or HTTP service, and knowing that precise version is essential for understanding the attack vector and planning remediation. On the Certified Ethical Hacker CEH exam, this concept tests your ability to map services during the reconnaissance and scanning phases, often appearing in scenario-based questions where you must choose the most effective Nmap feature for identifying a service rather than just an open port. A common trap is confusing -sV with -sS (SYN stealth scan) or -O (OS detection), but remember that -sV digs into the application layer. Memory tip: think “V for Version” to always pair service identification with the -sV flag.
CEH Footprinting, Reconnaissance and Scanning Practice Question
This CEH practice question tests your understanding of footprinting, reconnaissance and scanning. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A security team detects unusual outbound traffic from a host that appears to be a reverse shell. Which of the following Nmap features would be MOST effective for identifying the service running on the listening port of the command-and-control server?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Service version detection using the -sV flag
Option D is correct because the -sV flag instructs Nmap to perform service version detection by probing open ports and analyzing the responses to determine the exact application and version running on the listening port. In a reverse shell scenario, identifying the service (e.g., a specific SSH, HTTP, or custom listener) on the C2 server is critical for understanding the attack vector and planning remediation.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
UDP scan using the -sU flag
Why it's wrong here
UDP scan checks for open UDP ports, but reverse shells typically use TCP. Moreover, it does not identify service versions.
✗
Nmap Scripting Engine (NSE) with the http-enum script
Why it's wrong here
http-enum enumerates HTTP directories and files, not service identification on arbitrary ports.
✗
OS fingerprinting using the -O flag
Why it's wrong here
OS fingerprinting identifies the operating system, not the specific service running on a port.
✓
Service version detection using the -sV flag
Why this is correct
-sV probes open ports and compares responses to identify service names and versions, which is ideal for identifying a reverse shell service.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse OS fingerprinting (-O) with service version detection (-sV), thinking that identifying the OS will reveal the service, but the CEH exam emphasizes that -sV is the dedicated flag for service and version identification on listening ports.
Detailed technical explanation
How to think about this question
Service version detection (-sV) works by sending a series of probes (e.g., NULL, FIN, or application-specific payloads) to an open port and comparing the responses against Nmap's nmap-service-probes database, which contains signatures for thousands of services. In a real-world incident, the C2 server might be running a non-standard service on a high port, and -sV can often identify it even if it deviates slightly from the expected banner, though heavily obfuscated or custom listeners may evade detection.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the CEH exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Footprinting, Reconnaissance and Scanning — This question tests Footprinting, Reconnaissance and Scanning — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Service version detection using the -sV flag — Option D is correct because the -sV flag instructs Nmap to perform service version detection by probing open ports and analyzing the responses to determine the exact application and version running on the listening port. In a reverse shell scenario, identifying the service (e.g., a specific SSH, HTTP, or custom listener) on the C2 server is critical for understanding the attack vector and planning remediation.
What should I do if I get this CEH question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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