Things are much better than what they used to be. AWS Config is easy to setup and can be used to warn for that type of access-control issues. It's a good layer

Things are much better than what they used to be. AWS Config is easy to setup and can be used to warn for that type of access-control issues. It's a good layer of additional defense. The new S3 UI is also much better and won't let you do insecure things by default. AWS also sends emails when they find an open bucket. I don't know exactly when those are triggered but I got them in the past.