The correct answer is to change the SSH rule to allow from a specific IP range used by the company’s administrators. This is because SSH access should never be open to the entire internet (0.0.0.0/0), as it exposes the server to brute-force attacks and unauthorized login attempts; security group best practices for SSH restriction dictate that only trusted, known IP addresses—such as a corporate VPN or bastion host—should be permitted. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the principle of least privilege for network access, often appearing as a straightforward trap where candidates might mistakenly choose to remove SSH entirely or leave it wide open. A common memory tip is “SSH is not for the world”—always lock it down to a specific CIDR block, and remember that HTTP/HTTPS can be public, but management ports must be private.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 engineer is reviewing the security group rules for a web server. The security group currently has the following inbound rules: allow HTTP from 0.0.0.0/0, allow HTTPS from 0.0.0.0/0, and allow SSH from 0.0.0.0/0. Which change should the engineer make to improve security?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the SSH rule to allow from a specific IP range used by the company's administrators.
Option D is correct. SSH should be restricted to specific IPs (e.g., corporate network) to prevent unauthorized access. Option A is unnecessary if the rules already exist. Option B would break functionality. Option C is not sufficient; SSH should be restricted.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Remove the HTTP rule and keep only HTTPS.
Why it's wrong here
HTTP may be needed for redirects or legacy clients.
✗
Change the SSH rule to allow from the VPC CIDR only.
Why it's wrong here
If administrators are not in the VPC, they cannot connect.
✓
Change the SSH rule to allow from a specific IP range used by the company's administrators.
ICMP is not necessary and increases the attack surface.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Change the SSH rule to allow from a specific IP range used by the company's administrators. — Option D is correct. SSH should be restricted to specific IPs (e.g., corporate network) to prevent unauthorized access. Option A is unnecessary if the rules already exist. Option B would break functionality. Option C is not sufficient; SSH should be restricted.
What should I do if I get this SCS-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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