This rule is designed to detect unauthorized changes to AWS S3 bucket policies that could expose sensitive data to external accounts. Adversaries may exploit S3 bucket policies by using the `PutBucketPolicy` API call to grant permissions to an external account, allowing potential data exfiltration or further access to malicious actors. The rule specifically looks for changes where the policy includes an `Effect=Allow` statement without the AWS account ID of the bucket owner. Such changes signal that the bucket may be shared insecurely, which can indicate both malicious activity or misconfigurations requiring immediate investigation.