Bucket ACL grants WRITE_ACP permission to AWS users

Description

Unprotected S3 buckets are one of the major causes of data theft and intrusions. An S3 bucket that allows WRITE_ACP access to AWS users can provide attackers the ability to modify the ACL for the applicable bucket, which can lead to: S3 data loss, unintended changes to applications using that bucket, and unexpected charges. The only S3 buckets that should be globally accessible for unauthenticated users or for Any AWS Authenticate Users are those used for hosting static websites. Bucket ACL helps manage access to S3 bucket data.

We recommend AWS S3 buckets are not accessible to AWS users for WRITE_ACP actions to protect S3 data from unauthorized users and exposing sensitive data to public access.

Fix - Runtime

Procedure

S3 buckets should be protected by using the bucket ACL and bucket policies. If you want to share data with other users via S3 buckets, you could create pre-signed URLs with a short expiration duration.

To generate a pre-signed URL for the file samplefile.zip, use the following command:

aws s3 presign --expires-in 36000 s3://sharedfolder/samplefile.zip

To generate pre-signed URLS for every object in an S3 bucket, use the following command:

aws s3 ls --recursive s3://sharedfolder | awk '{print $4}' | 
while read line; do aws s3 presign --expires-in 36000 s3://sharedfolder/$line; done

📘 Note

For all automation-related work use the bucket policy and grant access to the required roles.

CLI Command

See Procedure above for CLI commands to use to fix this policy error.