There are big signs on world-accessible buckets when you go into the S3 console. It's a fairly new thing but they are (slowly) trying to help auditing and findi

There are big signs on world-accessible buckets when you go into the S3 console. It's a fairly new thing but they are (slowly) trying to help auditing and finding these things I guess. However I'm not sure if there are any built-in tools to find weird nested policies attached that could cause a similar permission to be granted to all..