S3 bucket ACL allows read or write to all users

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Metadata

Id: 07dda8de-d90d-469e-9b37-1aca53526ced

Cloud Provider: AWS

Platform: CloudFormation

Severity: Critical

Category: Access Control

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Description

S3 buckets must not use a public read-write ACL because it allows anyone on the internet to read, upload, modify, or delete objects. This risks data exposure, integrity loss, and service abuse. Check AWS::S3::Bucket resources and ensure the AccessControl property is not set to PublicReadWrite. Resources with AccessControl: PublicReadWrite will be flagged. Set AccessControl to Private or omit the ACL and enforce least-privilege access using bucket policies and a PublicAccessBlockConfiguration (enable BlockPublicAcls, IgnorePublicAcls, BlockPublicPolicy, and RestrictPublicBuckets) to prevent accidental public access.

Secure configuration example:

MyBucket:
  Type: AWS::S3::Bucket
  Properties:
    BucketName: my-bucket
    AccessControl: Private
    PublicAccessBlockConfiguration:
      BlockPublicAcls: true
      IgnorePublicAcls: true
      BlockPublicPolicy: true
      RestrictPublicBuckets: true

Compliant Code Examples

AWSTemplateFormatVersion: 2010-09-09
Description: Creating S3 bucket
Resources:
  JenkinsArtifacts03:
    Type: AWS::S3::Bucket
    Properties:
      AccessControl: BucketOwnerFullControl
      BucketName: jenkins-artifacts
      VersioningConfiguration:
        Status: Enabled
      Tags:
        - Key: CostCenter
          Value: ITEngineering
        - Key: Type
          Value: CICD

{
  "Resources": {
    "JenkinsArtifacts05": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "AccessControl": "PublicRead",
        "BucketName": "jenkins-secret-artifacts2",
        "VersioningConfiguration": {
          "Status": "Enabled"
        },
        "Tags": [
          {
            "Key": "CostCenter",
            "Value": "ITEngineering"
          }
        ]
      }
    }
  },
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "Creating S3 bucket"
}

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "Creating S3 bucket",
  "Resources": {
    "JenkinsArtifacts04": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "Tags": [
          {
            "Key": "CostCenter",
            "Value": ""
          }
        ],
        "AccessControl": "Private",
        "BucketName": "jenkins-secret-artifacts",
        "VersioningConfiguration": {
          "Status": "Enabled"
        }
      }
    }
  }
}

Non-Compliant Code Examples

AWSTemplateFormatVersion: 2010-09-09
Description: Creating S3 bucket
Resources:
  StaticPage01:
    Type: AWS::S3::Bucket
    Properties:
      AccessControl: PublicReadWrite
      BucketName: public-read-static-page01
      WebsiteConfiguration:
        ErrorDocument: 404.html
        IndexDocument: index.html
      Tags:
        - Key: CostCenter
          Value: ITEngineering

AWSTemplateFormatVersion: 2010-09-09
Description: Creating S3 bucket
Resources:
  JenkinsArtifacts02:
    Type: AWS::S3::Bucket
    Properties:
      AccessControl: PublicReadWrite
      BucketName: jenkins-artifacts-block-public
      PublicAccessBlockConfiguration:
        BlockPublicPolicy: false
      VersioningConfiguration:
        Status: Enabled
      Tags:
        - Key: CostCenter
          Value: ITEngineering
        - Key: Type
          Value: CICD

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "Creating S3 bucket",
  "Resources": {
    "JenkinsArtifacts01": {
      "Properties": {
        "Tags": [
          {
            "Key": "CostCenter",
            "Value": "ITEngineering"
          }
        ],
        "AccessControl": "PublicReadWrite",
        "BucketName": "jenkins-artifacts"
      },
      "Type": "AWS::S3::Bucket"
    }
  }
}