- A
Modify the network ACL of the subnet to deny outbound traffic to the malicious IP.
Why wrong: Network ACL affects all instances in the subnet, not just the compromised one.
- B
Change the route table of the subnet to route traffic to a blackhole.
Why wrong: Route table changes affect all instances in the subnet.
- C
Terminate the compromised EC2 instance immediately.
Why wrong: Termination is irreversible and may not be the fastest if you need to preserve data.
- D
Modify the security group attached to the instance to revoke all outbound rules.
Security group changes apply immediately to the instance and do not affect others.
Question 871 of 1,748
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 company's security team discovers that an Amazon EC2 instance has been compromised and is sending outbound traffic to a known malicious IP address. The instance is in a VPC with a security group that allows all outbound traffic. What is the FASTEST way to stop the outbound traffic without affecting other instances?
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
✓
Modify the security group attached to the instance to revoke all outbound rules.
Option D is correct because security groups are stateful and act as a virtual firewall at the instance level. By revoking all outbound rules in the security group attached to the compromised EC2 instance, you immediately block all outbound traffic from that specific instance without affecting any other instances in the VPC. This is the fastest and most targeted action because it requires no changes to subnet-level configurations or instance termination.
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.
- ✗
Modify the network ACL of the subnet to deny outbound traffic to the malicious IP.
Why it's wrong here
Network ACL affects all instances in the subnet, not just the compromised one.
- ✗
Change the route table of the subnet to route traffic to a blackhole.
Why it's wrong here
Route table changes affect all instances in the subnet.
- ✗
Terminate the compromised EC2 instance immediately.
Why it's wrong here
Termination is irreversible and may not be the fastest if you need to preserve data.
- ✓
Modify the security group attached to the instance to revoke all outbound rules.
Why this is correct
Security group changes apply immediately to the instance and do not affect others.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse security groups with network ACLs, assuming that a NACL change is faster or more precise, when in fact security groups are instance-level and can be modified instantly without affecting other instances, making them the fastest and most targeted solution.
Detailed technical explanation
How to think about this question
Security groups are stateful, meaning that if you allow inbound traffic, the outbound return traffic is automatically allowed regardless of outbound rules. However, when you revoke all outbound rules, the security group will deny any new outbound connections initiated by the instance, while still allowing return traffic for existing connections due to stateful tracking. This behavior is defined by the AWS VPC networking model and is distinct from NACLs, which are stateless and require explicit rules for each direction.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this SCS-C02 question test?
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Modify the security group attached to the instance to revoke all outbound rules. — Option D is correct because security groups are stateful and act as a virtual firewall at the instance level. By revoking all outbound rules in the security group attached to the compromised EC2 instance, you immediately block all outbound traffic from that specific instance without affecting any other instances in the VPC. This is the fastest and most targeted action because it requires no changes to subnet-level configurations or instance termination.
What should I do if I get this SCS-C02 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: Jul 4, 2026
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