- A
Attach an internet gateway (IGW) to the VPC and enable auto-assign public IP on the subnet.
Why wrong: An IGW is needed for internet access but does not filter traffic.
- B
Configure a network ACL on the subnet to allow inbound TCP ports 80 and 443 from 0.0.0.0/0 and deny inbound TCP port 22.
Network ACLs are stateless and provide subnet-level filtering; allowing HTTP/HTTPS and denying SSH adds defense.
- C
Place the web server in a private subnet and use a NAT gateway for outbound traffic.
Why wrong: A private subnet cannot receive inbound internet traffic without additional components like a load balancer.
- D
Configure a security group that allows inbound TCP port 443 from 0.0.0.0/0 and denies inbound TCP port 22.
Security groups are stateful and can allow/deny traffic. Allowing HTTPS and implicitly denying SSH meets the requirement.
- E
Deploy a web application firewall (WAF) in front of the web server.
Why wrong: A WAF protects against web exploits, not port-based access control.
CV0-004 Security Practice Question
This CV0-004 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 cloud administrator is configuring a new virtual private cloud (VPC) with a public subnet for a web application. The administrator must ensure that the web application can receive HTTPS traffic from the internet but cannot be directly accessed via SSH. Which TWO security controls should the administrator implement? (Choose two.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Configure a network ACL on the subnet to allow inbound TCP ports 80 and 443 from 0.0.0.0/0 and deny inbound TCP port 22.
Option B is correct because a network ACL (NACL) is a stateless firewall that operates at the subnet level, allowing you to explicitly deny inbound TCP port 22 (SSH) while allowing TCP ports 80 and 443 (HTTP/HTTPS) from 0.0.0.0/0. Option D is correct because a security group (SG) is a stateful firewall at the instance level; by default, SGs deny all inbound traffic, so you must explicitly allow TCP port 443 from 0.0.0.0/0, and since SSH (port 22) is not allowed, it is implicitly denied. Together, these provide defense-in-depth: the NACL blocks SSH at the subnet boundary, and the SG ensures only HTTPS is permitted to the web server.
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.
- ✗
Attach an internet gateway (IGW) to the VPC and enable auto-assign public IP on the subnet.
Why it's wrong here
An IGW is needed for internet access but does not filter traffic.
- ✓
Configure a network ACL on the subnet to allow inbound TCP ports 80 and 443 from 0.0.0.0/0 and deny inbound TCP port 22.
- ✗
Place the web server in a private subnet and use a NAT gateway for outbound traffic.
Why it's wrong here
A private subnet cannot receive inbound internet traffic without additional components like a load balancer.
- ✓
Configure a security group that allows inbound TCP port 443 from 0.0.0.0/0 and denies inbound TCP port 22.
- ✗
Deploy a web application firewall (WAF) in front of the web server.
Why it's wrong here
A WAF protects against web exploits, not port-based access control.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between stateless (NACL) and stateful (security group) firewalls, and the trap here is that candidates may think a security group alone is sufficient to deny SSH, forgetting that a permissive NACL could allow SSH traffic to reach the subnet, or they may incorrectly assume a WAF can block SSH at the network layer.
Detailed technical explanation
How to think about this question
Network ACLs are stateless, meaning you must explicitly allow both inbound and outbound traffic; for example, allowing inbound TCP 443 from 0.0.0.0/0 requires a corresponding outbound rule for ephemeral ports (1024-65535) to 0.0.0.0/0. Security groups are stateful, so if you allow inbound HTTPS, the return traffic is automatically permitted regardless of outbound rules. In a real-world scenario, using only a security group might still leave the instance exposed if the subnet NACL is too permissive, so combining both provides layered security—a common best practice in cloud architecture.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this CV0-004 question test?
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure a network ACL on the subnet to allow inbound TCP ports 80 and 443 from 0.0.0.0/0 and deny inbound TCP port 22. — Option B is correct because a network ACL (NACL) is a stateless firewall that operates at the subnet level, allowing you to explicitly deny inbound TCP port 22 (SSH) while allowing TCP ports 80 and 443 (HTTP/HTTPS) from 0.0.0.0/0. Option D is correct because a security group (SG) is a stateful firewall at the instance level; by default, SGs deny all inbound traffic, so you must explicitly allow TCP port 443 from 0.0.0.0/0, and since SSH (port 22) is not allowed, it is implicitly denied. Together, these provide defense-in-depth: the NACL blocks SSH at the subnet boundary, and the SG ensures only HTTPS is permitted to the web server.
What should I do if I get this CV0-004 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.
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Last reviewed: Jun 30, 2026
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