The correct answer is that SSH access is allowed from a broad internal CIDR block (10.0.0.0/8), which unnecessarily exposes the instance to internal threats. This is a security risk because the 10.0.0.0/8 range encompasses over 16 million IP addresses, meaning any compromised host within that vast internal network could potentially reach port 22. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the principle of least privilege for security group rules, specifically that even internal CIDRs should be scoped to the smallest necessary range, such as a specific VPC subnet like 10.0.1.0/24. A common trap is confusing overly permissive internal rules with the more obvious external 0.0.0.0/0, but the exam frequently hides risks inside seemingly private ranges. Remember the memory tip: “Don’t let your internal guard down—narrow the CIDR to your own town.”
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH access is allowed from a large internal CIDR block (10.0.0.0/8) which could expose the instance to unnecessary internal threats.
Option C is correct. The SSH port (22) is open to the internal CIDR block 10.0.0.0/8, which is unnecessarily broad. It should be restricted to specific IPs or a security group. Option A is incorrect because HTTP (80) to 0.0.0.0/0 is common for web servers. Option B is incorrect because the template uses a SecurityGroup property, not a SecurityGroupIds property. Option D is incorrect because the template does reference a security group.
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.
✗
The template does not associate the security group with the instance, so the instance has no security group.
Why it's wrong here
The template does associate via Ref.
✗
HTTP access is allowed from all IP addresses (0.0.0.0/0) which is a security risk.
Why it's wrong here
HTTP to 0.0.0.0/0 is typical for public web servers; not necessarily a risk.
✓
SSH access is allowed from a large internal CIDR block (10.0.0.0/8) which could expose the instance to unnecessary internal threats.
Why this is correct
10.0.0.0/8 is a large range; should be more restrictive.
The template uses SecurityGroups property instead of SecurityGroupIds, which is deprecated.
Why it's wrong here
SecurityGroups is still valid for EC2-Classic, but in VPC, SecurityGroupIds is recommended but not a security risk.
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: SSH access is allowed from a large internal CIDR block (10.0.0.0/8) which could expose the instance to unnecessary internal threats. — Option C is correct. The SSH port (22) is open to the internal CIDR block 10.0.0.0/8, which is unnecessarily broad. It should be restricted to specific IPs or a security group. Option A is incorrect because HTTP (80) to 0.0.0.0/0 is common for web servers. Option B is incorrect because the template uses a SecurityGroup property, not a SecurityGroupIds property. Option D is incorrect because the template does reference a security group.
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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