The answer is enabling AWS CloudTrail and Amazon GuardDuty for monitoring, because this measure is a detective control rather than a preventive one. While CloudTrail logs API calls and GuardDuty identifies threats, neither can block the root cause of the incident—a bucket policy that granted anonymous read access. The other proposed controls directly prevent unauthorized access: IAM roles enforce least privilege, KMS encryption protects data at rest, VPC isolation restricts network paths, and explicit deny policies in S3 block anonymous requests. On the CISSP exam, this question tests your ability to distinguish preventive controls (which stop incidents before they occur) from detective controls (which identify incidents after the fact). A common trap is to assume that monitoring alone can prevent misconfigurations, but the CISSP domain of Security Architecture and Engineering emphasizes that detective controls are reactive. Memory tip: “Detect doesn’t deflect”—monitoring catches breaches but cannot block the door that was left open.
CISSP Security Architecture and Engineering Practice Question
This CISSP practice question tests your understanding of security architecture and engineering. 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.
A financial services company has a hybrid cloud environment with on-premises servers and a public cloud provider. The security team recently discovered that an attacker exfiltrated sensitive customer data from a cloud storage bucket. The investigation reveals that the bucket was configured with a bucket policy that allowed anonymous read access. The security architect must redesign the architecture to prevent such incidents. The company uses AWS for cloud services. The architect proposes the following: (1) Enable AWS CloudTrail and Amazon GuardDuty for monitoring. (2) Implement AWS Identity and Access Management (IAM) roles for applications instead of long-term access keys. (3) Use AWS Key Management Service (KMS) to encrypt data at rest. (4) Configure a VPC with a NAT gateway and private subnets for all compute resources. (5) Implement S3 bucket policies that deny all access unless explicitly allowed by a specific IAM role. During a review, the chief information security officer (CISO) points out that one of these measures does not directly address the root cause of the incident. Which measure is least effective in preventing unauthorized access to S3 buckets?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Why wrong: Encryption protects data if accessed, but anonymous read can still exfiltrate encrypted data; the cloud provider decrypts for authorized requests.
B
Configure a VPC with private subnets and a NAT gateway
Why wrong: VPC design does not control S3 bucket policies; S3 access is independent of subnet type.
C
Enable AWS CloudTrail and Amazon GuardDuty for monitoring
Monitoring detects but does not prevent misconfigurations.
D
Implement IAM roles for applications instead of long-term access keys
Why wrong: Reduces risk of key compromise but does not prevent anonymous bucket access.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable AWS CloudTrail and Amazon GuardDuty for monitoring
Option C (enabling AWS CloudTrail and Amazon GuardDuty) is a detective control, not a preventive one. The root cause of the incident was a misconfigured bucket policy that allowed anonymous read access. Monitoring tools can detect unauthorized access after it occurs but cannot prevent it. The other options directly address the root cause by enforcing least privilege, encrypting data, or restricting network access.
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.
✗
Use AWS KMS to encrypt data at rest
Why it's wrong here
Encryption protects data if accessed, but anonymous read can still exfiltrate encrypted data; the cloud provider decrypts for authorized requests.
✗
Configure a VPC with private subnets and a NAT gateway
Why it's wrong here
VPC design does not control S3 bucket policies; S3 access is independent of subnet type.
✓
Enable AWS CloudTrail and Amazon GuardDuty for monitoring
Why this is correct
Monitoring detects but does not prevent misconfigurations.
Clue confirmation
The clue word "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Implement IAM roles for applications instead of long-term access keys
Why it's wrong here
Reduces risk of key compromise but does not prevent anonymous bucket access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing detective controls (monitoring) with preventive controls (access policies, encryption, network segmentation), leading candidates to think that enabling logging and threat detection directly prevents the root cause of a misconfigured bucket policy.
Detailed technical explanation
How to think about this question
S3 bucket policies are evaluated at the resource level and can grant or deny access based on principal, action, and condition keys. Anonymous access is explicitly allowed when the `Principal` element is set to `"*"` without a condition requiring authentication. AWS KMS provides envelope encryption using a customer master key (CMK) and data keys, but it does not enforce access control—that is the role of IAM and bucket policies. VPC endpoints (gateway or interface) can restrict S3 access to specific VPCs, but a NAT gateway alone does not restrict S3 access because S3 API calls go over the public internet unless a VPC endpoint is used.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Security Architecture and Engineering — This question tests Security Architecture and Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Enable AWS CloudTrail and Amazon GuardDuty for monitoring — Option C (enabling AWS CloudTrail and Amazon GuardDuty) is a detective control, not a preventive one. The root cause of the incident was a misconfigured bucket policy that allowed anonymous read access. Monitoring tools can detect unauthorized access after it occurs but cannot prevent it. The other options directly address the root cause by enforcing least privilege, encrypting data, or restricting network access.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "least". You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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