Account IDs are 12 digit random numbers. They are used to identify an AWS account, that's all. Knowledge of the full 12 digits doesn't grant access to anything,

Account IDs are 12 digit random numbers. They are used to identify an AWS account, that's all. Knowledge of the full 12 digits doesn't grant access to anything, prove you own the account, or enable you to authenticate to any systems (or individuals like in customer service for example) in AWS. They are visible when ever you share something with another AWS account, they're in the ARN. For example, the 12 digit account IDs of all a vendors that vend AMIs, assume roles on AWS accounts (think datadog, for logging / metrics) or otherwise provide services have AWS Account IDs that are well known and easily discoverable. This s3 example is just sort of interesting since its one of the handful of AWS services that don't use account IDs in ARNs. AWS account ids are not secrets and treating them as secrets or giving the impression that they are anything other than public data is a distraction from real security concerns.