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S3 bucket without ignore public ACL

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Metadata

Id: cloudformation-aws-s3-bucket-without-ignore-public-acl

Provider: AWS

Platform: CloudFormation

Severity: Medium

Category: Insecure Configurations

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Description

S3 buckets should ignore public ACLs to prevent object or bucket-level ACLs from granting unintended public access. Public ACLs can lead to accidental data exposure.

In CloudFormation, the AWS::S3::Bucket resource must include PublicAccessBlockConfiguration.IgnorePublicAcls and it must be set to true. Resources missing PublicAccessBlockConfiguration, missing the IgnorePublicAcls property, or with IgnorePublicAcls: false will be flagged.

Secure configuration example:

MyBucket:
  Type: AWS::S3::Bucket
  Properties:
    BucketName: my-bucket
    PublicAccessBlockConfiguration:
      IgnorePublicAcls: true

Compliant Code Examples

Resources:
  Bucket1:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls       : true
        BlockPublicPolicy     : true
        IgnorePublicAcls      : true
        RestrictPublicBuckets : true

Non-Compliant Code Examples

Resources:
  Bucket11:
    Type: AWS::S3::Bucket
    Properties:
---
Resources:
  Bucket12:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicPolicy     : true
        RestrictPublicBuckets : true
---
Resources:
  Bucket13:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls: false
        BlockPublicPolicy     : true
        IgnorePublicAcls      : false
        RestrictPublicBuckets : true