Rule: S3 Buckets should Prohibit Public Write Access
This rule ensures that S3 buckets do not allow public write access, maintaining data security
| Rule | S3 buckets should prohibit public write access |
| Framework | AWS Audit Manager Control Tower Guardrails |
| Severity | ✔ High |
Ensuring S3 Buckets Prohibit Public Write Access Following AWS Audit Manager Control Tower Guardrails
To enforce strong data security and comply with AWS Audit Manager Control Tower Guardrails, it's critical to make sure that Amazon S3 buckets within your AWS environments do not allow public write access. Here's how to approach setting up, verifying, and troubleshooting this rule:
Overview of the Rule
Public write access to S3 buckets can put your data at significant risk. AWS Audit Manager Control Tower Guardrails include mechanisms for ensuring that S3 buckets adhere to best practices for security, including the restriction of public write access.
Verification Steps
1. Review Bucket Policies and ACLs
Confirm that none of the bucket policies or access control lists (ACLs) grant public write access.
CLI Commands:
aws s3api get-bucket-policy --bucket YOUR_BUCKET_NAME aws s3api get-bucket-acl --bucket YOUR_BUCKET_NAME
2. Auditing with AWS Audit Manager
Utilize AWS Audit Manager to automate the auditing of your S3 buckets for compliance with the no public write access rule.
3. Check Public Access Block Configuration
Ensure the S3 bucket has the Public Access Block feature configured to block public ACLs and policies that allow public write access.
CLI Commands:
aws s3api get-public-access-block --bucket YOUR_BUCKET_NAME
Remediation Steps
If public write access is detected, perform the following steps to remediate:
1. Update Bucket Policy
Modify the bucket policy to explicitly deny public write access.
CLI Commands:
aws s3api put-bucket-policy --bucket YOUR_BUCKET_NAME --policy file://policy.json
2. Modify Bucket ACL
Change the bucket ACL to remove any grants that allow write access to the public.
CLI Commands:
aws s3api put-bucket-acl --bucket YOUR_BUCKET_NAME --acl private
3. Enable Public Access Block
Configure the S3 bucket to block new public ACLs and any policies that could allow public write access.
CLI Commands:
aws s3api put-public-access-block \ --bucket YOUR_BUCKET_NAME \ --public-access-block-configuration "BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true"
Troubleshooting Steps
1. Policy Does Not Take Effect
Ensure the policy is correctly formatted and that IAM permissions allow changes to bucket policies.
2. Access Denied Errors
Verify that your IAM user/role has the necessary permissions to modify S3 bucket policies and ACLs.
3. Uncertain about Public Access
Use the AWS S3 Console to visualize bucket permissions, or use AWS Trusted Advisor to review bucket permissions.
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