The correct answer is that SSH (port 22) is allowed from a large IP range, making this the most significant security concern. This is because permitting SSH access from a broad CIDR, such as 0.0.0.0/0, in a cloud VPC ACL exposes the management interface to the entire internet, enabling trivial brute-force or credential-stuffing attacks that violate the principle of least privilege. On the CISSP exam, this scenario tests your understanding of network segmentation and access control in cloud architectures, often appearing as a trap where examinees overlook the difference between a security group’s stateful filtering and an ACL’s stateless rules—remember, an ACL evaluates every packet in both directions. A quick memory tip: “Wide SSH is a wide risk—lock port 22 to a /32.”
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Refer to the exhibit. A security auditor is reviewing the network ACLs for a cloud VPC. Which of the following is the most significant security concern?
Why wrong: Outbound traffic restrictions are less critical; many environments allow outbound all. While not best practice, it's not the most significant concern compared to allowing SSH from a large range.
B
SSH (port 22) is allowed from a large IP range
Allowing SSH from 10.0.0.0/8 is overly broad and exposes administrative access to many potential attackers within that range.
C
RDP (port 3389) is allowed from a trusted internal subnet
Why wrong: RDP restricted to a specific internal subnet (192.168.1.0/24) is a reasonable security measure.
D
The VPC ID is exposed
Why wrong: The VPC ID is not sensitive information; it's often included in policy outputs and does not pose a risk.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH (port 22) is allowed from a large IP range
Allowing SSH (port 22) from a large IP range (e.g., 0.0.0.0/0 or a wide CIDR) exposes the management interface to the entire internet, making it trivial for attackers to launch brute-force or credential-stuffing attacks. This violates the principle of least privilege and is a common misconfiguration that leads to unauthorized access.
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.
✗
The outbound rules allow all traffic
Why it's wrong here
Outbound traffic restrictions are less critical; many environments allow outbound all. While not best practice, it's not the most significant concern compared to allowing SSH from a large range.
✓
SSH (port 22) is allowed from a large IP range
Why this is correct
Allowing SSH from 10.0.0.0/8 is overly broad and exposes administrative access to many potential attackers within that range.
Related concept
Read the scenario before looking for a memorised answer.
✗
RDP (port 3389) is allowed from a trusted internal subnet
Why it's wrong here
RDP restricted to a specific internal subnet (192.168.1.0/24) is a reasonable security measure.
✗
The VPC ID is exposed
Why it's wrong here
The VPC ID is not sensitive information; it's often included in policy outputs and does not pose a risk.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may focus on the outbound rule being too permissive (Option A) or the VPC ID exposure (Option D), but the most immediate and exploitable risk is the unrestricted inbound SSH access from a large IP range.
Trap categories for this question
Command / output trap
The VPC ID is not sensitive information; it's often included in policy outputs and does not pose a risk.
Detailed technical explanation
How to think about this question
SSH uses TCP port 22 and is a primary vector for remote server administration. When an ACL permits SSH from 0.0.0.0/0, any internet host can initiate a connection, leading to continuous brute-force attempts that can overwhelm authentication logs and, if credentials are weak, result in full system compromise. Cloud providers like AWS recommend using security groups with specific source IPs or bastion hosts to mitigate this risk.
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 analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: SSH (port 22) is allowed from a large IP range — Allowing SSH (port 22) from a large IP range (e.g., 0.0.0.0/0 or a wide CIDR) exposes the management interface to the entire internet, making it trivial for attackers to launch brute-force or credential-stuffing attacks. This violates the principle of least privilege and is a common misconfiguration that leads to unauthorized access.
What should I do if I get this CISSP 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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