Using the AWS Console, manually review the subscriber lists for SNS topics

Details

Center for Internet Security (CIS) Recommendation 3.15 is to Ensure appropriate subscribers to each SNS topic. https://d0.awsstatic.com/whitepapers/compliance/AWS_CIS_Foundations_Benchmark.pdf#page=130

This is a check that must be performed manually as there are either no appropriate API calls or it may require an account-specific judgement call.