The answer is that the Lambda execution role is missing SNS publish permissions. This is because an AWS Lambda function’s execution role defines the specific AWS service actions the function is authorized to perform; without an explicit `sns:Publish` action in the IAM policy, any attempt to send a message to an SNS topic will fail with an AccessDenied error, regardless of other configurations like the SQS trigger or queue policy. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of least-privilege permissions and the separation of concerns between resource-based policies and identity-based policies—a common trap is assuming that an SQS trigger or queue policy implicitly grants SNS access. Remember the memory tip: “Lambda can only do what its role says—if SNS isn’t listed, the publish is resisted.”
SCS-C02 Identity and Access Management Practice Question
This SCS-C02 practice question tests your understanding of identity and access management. 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 company has an AWS Lambda function that processes messages from an Amazon SQS queue. The Lambda function is configured with an execution role that has the following IAM policy:
The Lambda function is also configured with an SQS trigger that uses the same queue. The function code tries to send a message to an Amazon SNS topic, but the send fails with an AccessDenied error. 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 Lambda execution role does not have permissions to publish to SNS.
Option A is correct. The Lambda execution role does not include permissions to publish to SNS. The function can only perform actions that are allowed by the role. Option B is wrong because the SQS trigger does not affect the function's ability to call SNS. Option C is wrong because the SQS policy is not relevant to SNS. Option D is wrong because the SNS topic policy may not exist or may not deny; the error is due to missing IAM permissions.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 SQS queue has a resource-based policy that denies the Lambda function from sending to SNS.
Why it's wrong here
SQS queue policies do not control the function's outbound calls.
✓
The Lambda execution role does not have permissions to publish to SNS.
Why this is correct
The policy only grants SQS and CloudWatch Logs permissions, not SNS.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Standard ACLs match source addresses.
✗
The SNS topic has a resource-based policy that denies the Lambda function.
Why it's wrong here
While a topic policy could deny, the most likely cause is missing IAM permissions.
✗
The SQS queue is not configured to allow the Lambda function to send messages to SNS.
Why it's wrong here
SQS queue configuration does not affect the function's ability to call other services.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
Identity and Access Management — This question tests Identity and Access Management — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: The Lambda execution role does not have permissions to publish to SNS. — Option A is correct. The Lambda execution role does not include permissions to publish to SNS. The function can only perform actions that are allowed by the role. Option B is wrong because the SQS trigger does not affect the function's ability to call SNS. Option C is wrong because the SQS policy is not relevant to SNS. Option D is wrong because the SNS topic policy may not exist or may not deny; the error is due to missing IAM permissions.
What should I do if I get this SCS-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SCS-C02 ACL questions on filtering logic and placement.
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?
Standard ACLs match source addresses.
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