The answer is that the event pattern does not match the actual structure of GuardDuty findings. This is the most likely cause because CloudWatch Events rules require an exact JSON schema match to trigger a target; GuardDuty publishes findings with a specific nested structure under a `detail` object, including fields like `type`, `severity`, and a `source` value of `aws.guardduty`. If the rule’s event pattern uses incorrect field names, wrong nesting, or omits required elements, CloudWatch will silently discard the event as a non-match, so the Lambda function never fires. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of event-driven security automation and the precise schema of AWS service events—a common trap is assuming any partial pattern will work, or forgetting that `source` must be explicitly set. For a quick memory tip, remember “source, detail, and exact match”: the event pattern’s `source` must be `aws.guardduty`, the `detail` must mirror the finding’s JSON keys, and every field must match exactly or the rule stays silent.
SCS-C02 Threat Detection and Incident Response Practice Question
This SCS-C02 practice question tests your understanding of threat detection and incident response. 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.
Exhibit
Refer to the exhibit.
```
{
"source": ["aws.guardduty"],
"detail-type": ["GuardDuty Finding"],
"resources": ["arn:aws:ec2:us-east-1:123456789012:instance/i-0a1b2c3d4e5f67890"]
}
```
A security engineer creates an Amazon CloudWatch Events rule with this event pattern to trigger an AWS Lambda function for automated response to GuardDuty findings. However, the Lambda function is not triggered for new findings. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The event pattern does not match the actual structure of GuardDuty findings.
Option C is correct because the event pattern provided in the CloudWatch Events rule must exactly match the JSON structure of a GuardDuty finding as it is published to the default event bus. GuardDuty findings are delivered with a specific schema that includes a `detail` object containing `type`, `severity`, and other fields. If the event pattern uses incorrect field names, nesting, or missing required elements (e.g., `source` must be `aws.guardduty`), CloudWatch Events will not match the incoming events, and the Lambda function will not be triggered.
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 finding type is not specified in the pattern.
Why it's wrong here
Not required; pattern can match any finding type.
✗
CloudTrail is not enabled in the account.
Why it's wrong here
GuardDuty works independently of CloudTrail.
✓
The event pattern does not match the actual structure of GuardDuty findings.
Why this is correct
The `resources` field is an array of objects with `arn` property.
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 Lambda function does not have permission to be invoked by CloudWatch Events.
Why it's wrong here
Permissions are needed but pattern mismatch is more likely.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the issue is a missing permission (Option D) or a missing finding type (Option A), but AWS specifically designs this question to test whether you understand that CloudWatch Events pattern matching is strict and case-sensitive, and that GuardDuty findings have a predefined event structure that must be replicated exactly.
Detailed technical explanation
How to think about this question
GuardDuty findings are published as events with a `source` of `aws.guardduty` and a `detail-type` of `GuardDuty Finding`. The event pattern must use exact JSON paths, such as `{"source": ["aws.guardduty"]}`. A common mistake is using `"detail-type": "GuardDuty Finding"` without the hyphen or with incorrect casing. Under the hood, CloudWatch Events uses pattern matching against the event JSON; any deviation (e.g., extra whitespace, wrong key name) results in no match. In real-world scenarios, engineers often copy patterns from documentation but miss the required `detail-type` field, causing silent failures.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Threat Detection and Incident Response — This question tests Threat Detection and Incident Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The event pattern does not match the actual structure of GuardDuty findings. — Option C is correct because the event pattern provided in the CloudWatch Events rule must exactly match the JSON structure of a GuardDuty finding as it is published to the default event bus. GuardDuty findings are delivered with a specific schema that includes a `detail` object containing `type`, `severity`, and other fields. If the event pattern uses incorrect field names, nesting, or missing required elements (e.g., `source` must be `aws.guardduty`), CloudWatch Events will not match the incoming events, and the Lambda function will not be triggered.
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.
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.
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Question Discussion
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