This DBS-C01 practice question tests your understanding of database security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Refer to the exhibit. A security engineer has applied this key policy to a customer managed KMS key used to encrypt a Secrets Manager secret containing database credentials. An application running on an Amazon EC2 instance in the same account and region is unable to decrypt the secret. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
The condition kms:ViaService restricts the decryption to requests made via Secrets Manager, but the application is calling KMS directly.
This option is correct because the `kms:ViaService` condition restricts the `Decrypt` permission to only requests that originate from Secrets Manager. Since the application calls KMS directly, the condition is not satisfied, causing denial.
B
The KMS key ARN in the resource field is incorrect.
Why wrong: This option is incorrect because the KMS key ARN in the resource field is likely correct; the policy uses a wildcard or placeholder and the key is in the same account.
C
The policy is missing an encryption context that matches the secret's encryption context.
Why wrong: This option is incorrect because encryption contexts are not relevant to the issue; the policy does not require an encryption context for decryption.
D
The policy only allows Decrypt, but the application needs Encrypt permission.
Why wrong: This option is incorrect because the application only needs Decrypt permission to decrypt the secret; it does not need Encrypt.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The condition kms:ViaService restricts the decryption to requests made via Secrets Manager, but the application is calling KMS directly.
The condition `kms:ViaService` in the key policy restricts the `Decrypt` permission to requests that originate specifically from the AWS Secrets Manager service. When the application on the EC2 instance calls KMS directly (e.g., via the `Decrypt` API) to decrypt the secret, the request does not come through Secrets Manager, so the condition is not satisfied and the request is denied. This is the most likely cause of the decryption failure.
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 condition kms:ViaService restricts the decryption to requests made via Secrets Manager, but the application is calling KMS directly.
Why this is correct
This option is correct because the `kms:ViaService` condition restricts the `Decrypt` permission to only requests that originate from Secrets Manager. Since the application calls KMS directly, the condition is not satisfied, causing denial.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The KMS key ARN in the resource field is incorrect.
Why it's wrong here
This option is incorrect because the KMS key ARN in the resource field is likely correct; the policy uses a wildcard or placeholder and the key is in the same account.
✗
The policy is missing an encryption context that matches the secret's encryption context.
Why it's wrong here
This option is incorrect because encryption contexts are not relevant to the issue; the policy does not require an encryption context for decryption.
✗
The policy only allows Decrypt, but the application needs Encrypt permission.
Why it's wrong here
This option is incorrect because the application only needs Decrypt permission to decrypt the secret; it does not need Encrypt.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overlook the `kms:ViaService` condition and assume the policy is correct, focusing instead on encryption contexts or permissions, when the real issue is that the condition restricts the source of the request to a specific AWS service.
Detailed technical explanation
How to think about this question
The `kms:ViaService` condition key allows you to restrict KMS key usage to requests that are made on behalf of a specific AWS service (e.g., `secretsmanager.amazonaws.com`). When an application calls the KMS `Decrypt` API directly, the `CallerSource` is the EC2 instance's IAM role, not the Secrets Manager service, so the condition fails. In practice, to allow direct KMS calls, you must either remove the condition or add an additional `Allow` statement without the `kms:ViaService` restriction for the application's IAM role.
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.
Database Security — This question tests Database Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The condition kms:ViaService restricts the decryption to requests made via Secrets Manager, but the application is calling KMS directly. — The condition `kms:ViaService` in the key policy restricts the `Decrypt` permission to requests that originate specifically from the AWS Secrets Manager service. When the application on the EC2 instance calls KMS directly (e.g., via the `Decrypt` API) to decrypt the secret, the request does not come through Secrets Manager, so the condition is not satisfied and the request is denied. This is the most likely cause of the decryption failure.
What should I do if I get this DBS-C01 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Refer to the exhibit. A company has attached this IAM policy to an IAM role used by an application running on Amazon EC2. The application needs to decrypt data in an S3 bucket that is encrypted with the specified KMS key. However, the application is receiving access denied errors. What is the most likely cause?
medium
A.The policy does not include 'kms:Decrypt' for the specific key.
✓ B.The application is decrypting the data by calling KMS directly instead of using S3's server-side decryption.
C.The policy is missing a 'Principal' element.
D.The IAM role does not have a trust policy that allows EC2 to assume it.
Why B: The policy condition 'kms:ViaService' restricts KMS operations to only when they are made through S3. However, the condition also includes 'kms:CallerAccount' which is redundant but not harmful. The error likely occurs because the EC2 instance does not have the correct IAM role, or the policy is missing 'kms:Decrypt' for the specific ciphertext. But the most common mistake is that the application is not using the S3 service to decrypt; if the application reads the encrypted object and then calls KMS directly to decrypt, the 'kms:ViaService' condition will fail because the call is not via S3. Option B addresses this. Option A is wrong because the condition is present. Option C is wrong because the role is not explicitly denied. Option D is wrong because the policy allows KMS actions.
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Question Discussion
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