Predefined permissions, also known as canned ACLs,
are an easy way to grant large privileges to predefined groups or users.
The following canned ACLs are security-sensitive:
PublicReadWrite grant respectively "read" and "read and write" privileges to everyone in the world
AuthenticatedRead grants "read" privilege to all authenticated users (
Ask Yourself Whether
- The S3 bucket stores sensitive data.
- The S3 bucket is not used to store static resources of websites (images, css …).
There is a risk if you answered yes to any of those questions.
Recommended Secure Coding Practices
It’s recommended to implement the least privilege policy, ie to grant necessary permissions only to users for their required tasks. In the context
of canned ACL, set it to
private (the default one) and if needed more granularity then use an appropriate S3 policy.
Sensitive Code Example
All users (ie: anyone in the world authenticated or not) have read and write permissions with the
PublicReadWrite access control:
Type: 'AWS::S3::Bucket' # Sensitive
private access control (default), only the bucket owner has the read/write permissions on the buckets and its ACL.
Type: 'AWS::S3::Bucket' # Compliant