CEH Vulnerability Analysis and System Hacking Practice Question
This CEH practice question tests your understanding of vulnerability analysis and system hacking. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Exhibit
nmap -sV -p 22,80,443,3306 target.com
Starting Nmap 7.80 ( https://nmap.org ) at 2023-08-15 14:22 EDT
Nmap scan report for target.com (192.168.1.100)
Host is up (0.0012s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 7.4 (protocol 2.0)
80/tcp filtered http
443/tcp open ssl/http Apache httpd 2.4.6 ((CentOS) OpenSSL/1.0.2k-fips)
3306/tcp open mysql MySQL 5.6.50
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 15.67 seconds
Refer to the exhibit. During a penetration test, the results show port 80 as 'filtered'. Which of the following is the most likely reason?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Exhibit
nmap -sV -p 22,80,443,3306 target.com
Starting Nmap 7.80 ( https://nmap.org ) at 2023-08-15 14:22 EDT
Nmap scan report for target.com (192.168.1.100)
Host is up (0.0012s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 7.4 (protocol 2.0)
80/tcp filtered http
443/tcp open ssl/http Apache httpd 2.4.6 ((CentOS) OpenSSL/1.0.2k-fips)
3306/tcp open mysql MySQL 5.6.50
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 15.67 seconds
A
The SSH service is interfering with the scan.
Why wrong: SSH on port 22 does not affect scans of other ports.
B
The target host is offline.
Why wrong: The target is up (0.0012s latency), so it is not offline.
C
The web server is not running.
Why wrong: If the web server were not running, port 80 would show as 'closed', not 'filtered'.
D
A firewall or ACL is blocking the port.
'Filtered' in Nmap indicates that a firewall or packet filter is blocking the probe, preventing Nmap from determining whether the port is open or closed.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A firewall or ACL is blocking the port.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The SSH service is interfering with the scan.
Why it's wrong here
SSH on port 22 does not affect scans of other ports.
✗
The target host is offline.
Why it's wrong here
The target is up (0.0012s latency), so it is not offline.
✗
The web server is not running.
Why it's wrong here
If the web server were not running, port 80 would show as 'closed', not 'filtered'.
✓
A firewall or ACL is blocking the port.
Why this is correct
'Filtered' in Nmap indicates that a firewall or packet filter is blocking the probe, preventing Nmap from determining whether the port is open or closed.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Trap categories for this question
Command / output trap
If the web server were not running, port 80 would show as 'closed', not 'filtered'.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CEH question in full detail.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CEH ACL questions on filtering logic and placement.
Vulnerability Analysis and System Hacking — This question tests Vulnerability Analysis and System Hacking — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: A firewall or ACL is blocking the port.
What should I do if I get this CEH question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CEH ACL questions on filtering logic and placement.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Standard ACLs match source addresses.
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