AWSOverview
In AWS the prefered way to grant access to a bucket is by using Bucket Policies, but you can also grant access via Access Control Lists.
When creating a new bucket the ACLs are disabled by default, but if you wish to use them, ensure that they allow access only to specific AWS Accounts (following the least privilege principle). The only exceptions are publicly hosted websites and objects such as public documents and pictures.
Remediation guidance
AWS remediation
Prefer disabling ACLs and using policies/IAM.
Console
- Open S3 bucket permissions.
- Set Object Ownership to Bucket owner enforced.
- If ACLs must remain enabled, remove broad grants.
AWS CLI
aws s3api put-bucket-ownership-controls \
--bucket <bucket-name> \
--ownership-controls Rules=[{ObjectOwnership=BucketOwnerEnforced}]
References
- https://docs.aws.amazon.com/AmazonS3/latest/userguide/managing-acls.html
- https://docs.aws.amazon.com/AmazonS3/latest/userguide/about-object-ownership.html
- https://docs.aws.amazon.com/cli/latest/reference/s3api/put-bucket-ownership-controls.html
Service-wide remediation
Recommended when many resources are affected: fix the platform baseline first so new resources inherit the secure setting, then remediate the existing flagged resources in batches.
AWS
Use AWS Organizations guardrails, AWS Config rules or conformance packs where they fit, approved account baselines, and IaC modules so new resources inherit the secure setting.
Operational rollout
- Fix the baseline first at the account, subscription, project, cluster, or tenant scope that owns this control.
- Remediate the currently affected resources in batches, starting with internet-exposed and production assets.
- Re-scan and track approved exceptions with an owner and expiry date.
Query logic
These are the stored checks tied to this control.
S3 bucket ACL grants permissions only to specific AWS accounts
Connectors
Covered asset types
Expected check: eq []
{buckets(where:{hasBucketACLGrant_SOME: {granteeType_NOT:"CanonicalUser"}}){...AssetFragment}}
