Over the last few years there have been a large number of data breaches from S3 buckets, for example:
Some of the data breaches were simply due to the S3 bucket being configured as public instead of private. AWS improved the S3 console recently, to clearly warn the user when a bucket or object is being made public. But I know some DevOps engineers who only ever use code and never log in to the console - so they would never see these warnings.
The Dow Jones case I find interesting because the misconfiguration arose from the use of "authenticated users" in the access control list. You might think that means an authenticated user of the same AWS account the S3 bucket resides in. Actually it means any AWS account in the world.
The Uber S3 bucket wasn't misconfigured as such - it appears that an attacker got hold of GitHub credentials, so could access private Git repositories, the attacker then discovered an AWS key which had rights to the S3 bucket.
Effectively protecting an organisation against cloud security incidents such as these requires an in-depth understanding of cloud security architecture, security expertise relating to cloud provider services, combined with a DevSecOps approach to infrastructure code development, testing and deployment.