Ensure S3 bucket ACL grants permissions only to specific AWS accounts

Overview

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

Multiple Remediation Paths

AWS

SERVICE-WIDE (RECOMMENDED when many resources are affected): Deploy centralized guardrails and remediation using AWS Config Conformance Packs and (if applicable) AWS Organizations SCPs.

aws configservice put-organization-conformance-pack --organization-conformance-pack-name <pack-name> --template-s3-uri s3://<bucket>/<template>.yaml

ASSET-LEVEL: Apply the resource-specific remediation steps above to only the affected assets.

PREVENTIVE: Add CI/CD policy checks (CloudFormation/Terraform validation) before deployment to prevent recurrence.

References for Service-Wide Patterns

AWS Config Conformance Packs: https://docs.aws.amazon.com/config/latest/developerguide/conformance-packs.html
AWS Organizations SCP examples: https://docs.aws.amazon.com/organizations/latest/userguide/orgs_manage_policies_scps_examples.html

Operational Rollout Workflow

Use this sequence to reduce risk and avoid repeated drift.

1. Contain at Service-Wide Scope First (Recommended)

AWS: deploy/adjust organization conformance packs and policy guardrails.

aws configservice put-organization-conformance-pack --organization-conformance-pack-name <pack-name> --template-s3-uri s3://<bucket>/<template>.yaml

2. Remediate Existing Affected Assets

Execute the control-specific Console/CLI steps documented above for each flagged resource.
Prioritize internet-exposed and production assets first.

3. Validate and Prevent Recurrence

Re-scan after each remediation batch.
Track exceptions with owner and expiry date.
Add preventive checks in IaC/CI pipelines.

Query logic

These are the stored checks tied to this control.

S3 bucket ACL grants permissions only to specific AWS accounts

Connectors

AWS

Covered asset types

Bucket

Expected check: eq []

{buckets(where:{hasBucketACLGrant_SOME: {granteeType_NOT:"CanonicalUser"}}){...AssetFragment}}