The correct choice is to remove the inbound SSH rule and use AWS Systems Manager Session Manager to access the bastion host. This is more secure because Session Manager establishes a bidirectional connection through the AWS SSM agent without opening any inbound ports, eliminating the attack surface entirely and relying on IAM policies for granular access control rather than network rules. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the principle of least privilege and the shift from network-based to identity-based security—a common trap is thinking that changing the SSH port or restricting to a single IP is sufficient, but attackers scan all ports and a single IP can be spoofed. Remember the mnemonic: "No port, no problem—SSM kills the SSH attack surface."
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.
A security engineer notices that an Amazon EC2 instance has a security group that allows inbound SSH (port 22) from 0.0.0.0/0. The instance is a bastion host. What is a more secure alternative to this configuration?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Remove the inbound SSH rule and use AWS Systems Manager Session Manager to access the instance.
The correct answer is C because using AWS Systems Manager Session Manager allows SSH access without opening any inbound ports, and it uses IAM policies for access control. Option A is wrong because a NACL is stateless and would still require an inbound rule; also, NACLs are not a replacement for security group configuration. Option B is wrong because changing the port does not improve security; attackers scan all ports. Option D is wrong because restricting to a single IP is better than open to all, but Session Manager is more secure as it eliminates inbound ports entirely.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Change the SSH port to a non-standard port to avoid automated attacks.
Why it's wrong here
Changing the port is not a security best practice; it only obscures the service.
✗
Restrict the inbound SSH rule to a single IP address from the corporate network.
Why it's wrong here
This is better than open to all, but still requires an open inbound port. Session Manager is more secure.
✗
Replace the security group rule with a network ACL that allows SSH from 0.0.0.0/0.
Why it's wrong here
This does not improve security; it still allows all inbound traffic on port 22.
✓
Remove the inbound SSH rule and use AWS Systems Manager Session Manager to access the instance.
Why this is correct
Session Manager provides secure access without inbound ports, using IAM for authentication and authorization.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
Infrastructure Security — This question tests Infrastructure Security — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Remove the inbound SSH rule and use AWS Systems Manager Session Manager to access the instance. — The correct answer is C because using AWS Systems Manager Session Manager allows SSH access without opening any inbound ports, and it uses IAM policies for access control. Option A is wrong because a NACL is stateless and would still require an inbound rule; also, NACLs are not a replacement for security group configuration. Option B is wrong because changing the port does not improve security; attackers scan all ports. Option D is wrong because restricting to a single IP is better than open to all, but Session Manager is more secure as it eliminates inbound ports entirely.
What should I do if I get this SCS-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SCS-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Question Discussion
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