S3 buckets should ignore public ACLs to prevent object or bucket-level ACLs from granting unintended public access. Public ACLs can lead to accidental data exposure.
In CloudFormation, the AWS::S3::Bucket resource must include PublicAccessBlockConfiguration.IgnorePublicAcls and it must be set to true. Resources missing PublicAccessBlockConfiguration, missing the IgnorePublicAcls property, or with IgnorePublicAcls: false will be flagged.