S3 Bucket Access to Any Principal

• Query id: 7772bb8c-c0f3-42d4-8e4e-f1b8939ad085
• Query name: S3 Bucket Access to Any Principal
• Platform: CloudFormation
• Severity: Critical
• Category: Access Control
• URL: Github

Description

The S3 Bucket should not be associated with a policy statement that grants access to any principal
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

Resources:
  Bucket:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls: false
        BlockPublicPolicy: false
        IgnorePublicAcls: true
        RestrictPublicBuckets: false
  BucketPolicy:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket: !Ref Bucket
      PolicyDocument:
        Statement:
        - Effect: Allow
          Principal:
            AWS:
            - "*"
          Action: s3:GetObject
          Resource: arn:aws:s3:::DOC-EXAMPLE-BUCKET/*
          Condition:
            StringLike:
              'aws:Referer':
                - 'http://www.example.com/*'
                - 'http://example.net/*'
  Bucket2:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls: false
        BlockPublicPolicy: false
        IgnorePublicAcls: false
        RestrictPublicBuckets: true
  BucketPolicy2:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket: !Ref Bucket2
      PolicyDocument:
        Statement:
        - Effect: Allow
          Principal:
            AWS:
            - "*"
          Action: s3:GetObject
          Resource: arn:aws:s3:::DOC-EXAMPLE-BUCKET/*
          Condition:
            StringLike:
              'aws:Referer':
                - 'http://www.example.com/*'
                - 'http://example.net/*'

Positive test num. 2 - json file

{
  "Resources": {
    "Bucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "PublicAccessBlockConfiguration": {
          "BlockPublicAcls": false,
          "BlockPublicPolicy": false,
          "IgnorePublicAcls": true,
          "RestrictPublicBuckets": false
        }
      }
    },
    "BucketPolicy": {
      "Properties": {
        "PolicyDocument": {
          "Statement": [
            {
              "Effect": "Allow",
              "Principal": {
                "AWS": [
                  "*"
                ]
              },
              "Action": "s3:GetObject",
              "Resource": "arn:aws:s3:::DOC-EXAMPLE-BUCKET/*",
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              }
            }
          ]
        },
        "Bucket": "Bucket"
      },
      "Type": "AWS::S3::BucketPolicy"
    },
    "Bucket2": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "PublicAccessBlockConfiguration": {
          "BlockPublicAcls": false,
          "BlockPublicPolicy": false,
          "IgnorePublicAcls": false,
          "RestrictPublicBuckets": true
        }
      }
    },
    "BucketPolicy2": {
      "Type": "AWS::S3::BucketPolicy",
      "Properties": {
        "Bucket": "Bucket2",
        "PolicyDocument": {
          "Statement": [
            {
              "Effect": "Allow",
              "Principal": {
                "AWS": [
                  "*"
                ]
              },
              "Action": "s3:GetObject",
              "Resource": "arn:aws:s3:::DOC-EXAMPLE-BUCKET/*",
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              }
            }
          ]
        }
      }
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

Resources:
  Bucket:
    Type: AWS::S3::Bucket
    Properties:
      PublicAccessBlockConfiguration:
        BlockPublicAcls: false
        BlockPublicPolicy: false
        IgnorePublicAcls: true
        RestrictPublicBuckets: true
  BucketPolicy:
    Type: AWS::S3::BucketPolicy
    Properties:
      Bucket: !Ref Bucket
      PolicyDocument:
        Statement:
        - Effect: Allow
          Principal:
            AWS:
            - arn:aws:iam::111122223333:user/Alice
            - arn:aws:iam::111122223333:user/foo
          Action: s3:GetObject
          Resource: arn:aws:s3:::DOC-EXAMPLE-BUCKET/*
          Condition:
            StringLike:
              'aws:Referer':
                - 'http://www.example.com/*'
                - 'http://example.net/*'

Negative test num. 2 - json file

{
  "Resources": {
    "Bucket": {
      "Type": "AWS::S3::Bucket",
      "Properties": {
        "PublicAccessBlockConfiguration": {
          "BlockPublicAcls": false,
          "BlockPublicPolicy": false,
          "IgnorePublicAcls": true,
          "RestrictPublicBuckets": true
        }
      }
    },
    "BucketPolicy": {
      "Type": "AWS::S3::BucketPolicy",
      "Properties": {
        "PolicyDocument": {
          "Statement": [
            {
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              },
              "Effect": "Allow",
              "Principal": {
                "AWS": [
                  "arn:aws:iam::111122223333:user/Alice",
                  "arn:aws:iam::111122223333:user/foo"
                ]
              },
              "Action": "s3:GetObject",
              "Resource": "arn:aws:s3:::DOC-EXAMPLE-BUCKET/*"
            }
          ]
        },
        "Bucket": "Bucket"
      }
    }
  }
}