The correct rule set is to allow inbound TCP 443 to 10.1.1.10, allow outbound TCP from 10.1.1.10, and deny all inbound. This works because HTTPS exclusively uses TCP port 443 for encrypted web traffic, and the outbound rule permits the server’s stateful responses—either explicitly or via a stateful firewall—while the final deny-all ensures no other inbound protocols or ports reach the server. On the CompTIA SecurityX CAS-004 exam, this scenario tests your understanding of least-privilege access control and the distinction between stateless and stateful rule placement; a common trap is forgetting to allow the return traffic or accidentally blocking it with a broad deny rule. Remember that a firewall rule to allow inbound HTTPS only must specify the destination IP and port, permit the corresponding outbound traffic, and then drop everything else—think of it as “443 in, any out, deny the rest.” A useful mnemonic is “HTTPS: 443 in, server out, block the doubt.”
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security engineering. 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 network administrator is configuring a firewall rule set. The requirement is to allow inbound HTTPS traffic from the internet to a web server at 10.1.1.10, and to allow the web server to respond. All other inbound traffic should be blocked. Which rule set accomplishes this?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Allow inbound TCP 443 to 10.1.1.10; allow outbound TCP from 10.1.1.10; deny all inbound
Option B is correct because HTTPS uses TCP port 443, and the rule set correctly allows inbound TCP 443 to the web server at 10.1.1.10, permits the server's outbound responses (stateful or explicit), and then denies all other inbound traffic. This matches the requirement to allow only HTTPS traffic from the internet while blocking everything else.
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.
✗
Allow inbound TCP 80 to 10.1.1.10; allow outbound TCP from 10.1.1.10; deny all inbound
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overlook rule order and choose Option C, thinking a 'deny all' at the top is safe, but it actually blocks the intended traffic before the allow rule is processed.
Detailed technical explanation
How to think about this question
Firewalls process rules sequentially from top to bottom, so rule order is critical; a 'deny all' rule placed before an allow rule will block the allowed traffic. Stateful firewalls automatically permit return traffic for established connections, but explicit outbound allow rules are often used for clarity or in stateless environments. In real-world scenarios, misordering rules is a common misconfiguration that can lead to security gaps or service outages.
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 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security Engineering — This question tests Security Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Allow inbound TCP 443 to 10.1.1.10; allow outbound TCP from 10.1.1.10; deny all inbound — Option B is correct because HTTPS uses TCP port 443, and the rule set correctly allows inbound TCP 443 to the web server at 10.1.1.10, permits the server's outbound responses (stateful or explicit), and then denies all other inbound traffic. This matches the requirement to allow only HTTPS traffic from the internet while blocking everything else.
What should I do if I get this CAS-004 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.
About these practice questions
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Variation 1. A network administrator is configuring a firewall to allow only necessary traffic to a web server. The server should be accessible from the internet on port 443 and from a management subnet on port 22. Which firewall rule ensures least privilege?
easy
A.Allow traffic from management subnet to port 443 and any to port 22
B.Allow traffic from any source to ports 443 and 22
C.Allow all traffic to the server, then block specific ports
✓ D.Allow traffic from any to port 443, and from management subnet to port 22; deny all else
Why D: Allow only specific ports from specific sources, and block all other traffic.
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Question Discussion
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