Security Group Outbound Rules: Least Privilege for Egress Traffic
This SCS-C02 practice question tests your understanding of infrastructure security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Network Topology
A security engineer sees the above security group configuration for an EC2 instance. The instance hosts a web application that should only be accessible from the internal network (10.0.0.0/8) over HTTPS, and SSH should not be open to the internet. What is the security issue with this configuration?
Network Topology
A
The outbound rule allows all traffic to all destinations.
The outbound rule allows all traffic to 0.0.0.0/0, which is overly permissive and could allow data exfiltration.
B
The inbound HTTPS rule is too permissive.
Why wrong: HTTPS is open to 0.0.0.0/0, but the requirement says it should be restricted to internal network. However, this is a misconfiguration, but the question may consider the outbound rule as the issue.
C
The inbound SSH rule is too permissive.
Why wrong: SSH is restricted to 10.0.0.0/8, which is appropriate.
D
There is no security issue; the configuration is correct.
Why wrong: There are issues with both inbound HTTPS and outbound rules.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The outbound rule allows all traffic to all destinations.
Option A is correct because the outbound rule allowing all traffic to all destinations (0.0.0.0/0) violates the principle of least privilege. While the inbound rules restrict HTTPS to the internal network (10.0.0.0/8) and SSH is not open to the internet, the outbound rule permits any instance in the security group to initiate connections to any IP address and port, including malicious external hosts. This could allow data exfiltration or outbound attacks, which is a security issue even if inbound access is properly restricted.
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 rule allows all traffic to all destinations.
Why this is correct
The outbound rule allows all traffic to 0.0.0.0/0, which is overly permissive and could allow data exfiltration.
Related concept
Read the scenario before looking for a memorised answer.
✗
The inbound HTTPS rule is too permissive.
Why it's wrong here
HTTPS is open to 0.0.0.0/0, but the requirement says it should be restricted to internal network. However, this is a misconfiguration, but the question may consider the outbound rule as the issue.
✗
The inbound SSH rule is too permissive.
Why it's wrong here
SSH is restricted to 10.0.0.0/8, which is appropriate.
✗
There is no security issue; the configuration is correct.
Why it's wrong here
There are issues with both inbound HTTPS and outbound rules.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus solely on inbound rules (HTTPS and SSH) and overlook the outbound rule, assuming that stateful security groups automatically handle outbound traffic safely, but AWS explicitly tests that outbound rules must also be restricted to follow least privilege.
Detailed technical explanation
How to think about this question
Security groups in AWS are stateful, meaning that if an inbound rule allows traffic, the outbound return traffic is automatically permitted regardless of outbound rules. However, outbound rules still control traffic initiated from the instance. An overly permissive outbound rule (0.0.0.0/0, all ports) allows the instance to connect to any external host, which could be exploited for command-and-control communication or data exfiltration if the instance is compromised. In a real-world scenario, an attacker who gains access to the web application could use this outbound rule to exfiltrate sensitive data to an external server, bypassing the inbound restrictions.
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 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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: The outbound rule allows all traffic to all destinations. — Option A is correct because the outbound rule allowing all traffic to all destinations (0.0.0.0/0) violates the principle of least privilege. While the inbound rules restrict HTTPS to the internal network (10.0.0.0/8) and SSH is not open to the internet, the outbound rule permits any instance in the security group to initiate connections to any IP address and port, including malicious external hosts. This could allow data exfiltration or outbound attacks, which is a security issue even if inbound access is properly restricted.
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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Variation 1. A security engineer runs the above AWS CLI command. The engineer notices that the security group has no outbound rules. What is the implication of this configuration?
medium
✓ A.The EC2 instances in this security group cannot initiate outbound connections
C.The security group allows all outbound traffic by default
D.Outbound traffic is allowed because security groups are stateful
Why A: Option A is correct because a security group without outbound rules will block all outbound traffic by default (since security groups are stateful and default deny egress). Option B is wrong because security groups are stateful; the inbound rule allows return traffic. Option C is wrong because the inbound rule allows HTTP from anywhere, but outbound is missing. Option D is wrong because the security group does allow inbound HTTP.
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Question Discussion
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