S3 Bucket Allows Get Action From All Principals

• Query id: f97b7d23-568f-4bcc-9ac9-02df0d57fbba
• Query name: S3 Bucket Allows Get Action From All Principals
• Platform: CloudFormation
• Severity: High
• Category: Access Control
• URL: Github

Description

S3 Buckets must not allow Get Action From All Principals, as to prevent leaking private information to the entire internet or allow unauthorized data tampering / deletion. This means the 'Effect' must not be 'Allow' when the 'Action' is Get, for all Principals.
Documentation

Code samples

Code samples with security vulnerabilities

Postitive test num. 1 - yaml file

#this is a problematic code where the query should report a result(s)
Resources:
  SampleBucketPolicy3:
    Type: 'AWS::S3::BucketPolicy'
    Properties:
      Bucket: !Ref DOC-EXAMPLE-BUCKET
      PolicyDocument:
        Statement:
          - Action: "GetObject"
            Effect: Allow
            Resource: "*"
            Principal: "*"
            Condition:
              StringLike:
                'aws:Referer':
                  - 'http://www.example.com/*'
                  - 'http://example.net/*'
  SampleBucketPolicy4:
    Type: 'AWS::S3::BucketPolicy'
    Properties:
      Bucket: !Ref DOC-EXAMPLE-BUCKET
      PolicyDocument:
        Statement:
          - Action:
              - "DeleteObject"
              - "GetObject"
            Effect: Allow
            Resource: "*"
            Principal: "*"
            Condition:
              StringLike:
                'aws:Referer':
                  - 'http://www.example.com/*'
                  - 'http://example.net/*'

Postitive test num. 2 - json file

{
  "Resources": {
    "SampleBucketPolicy5": {
      "Type": "AWS::S3::BucketPolicy",
      "Properties": {
        "Bucket": {
          "Ref": "DOC-EXAMPLE-BUCKET"
        },
        "PolicyDocument": {
          "Statement": [
            {
              "Action": "GetObject",
              "Effect": "Allow",
              "Resource": "*",
              "Principal": "*",
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              }
            }
          ]
        }
      }
    },
    "SampleBucketPolicy6": {
      "Type": "AWS::S3::BucketPolicy",
      "Properties": {
        "Bucket": {
          "Ref": "DOC-EXAMPLE-BUCKET"
        },
        "PolicyDocument": {
          "Statement": [
            {
              "Action": ["DeleteObject", "GetObject"],
              "Effect": "Allow",
              "Resource": "*",
              "Principal": "*",
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              }
            }
          ]
        }
      }
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

#this code is a correct code for which the query should not find any result
Resources:
  SampleBucketPolicy1:
    Type: 'AWS::S3::BucketPolicy'
    Properties:
      Bucket: !Ref DOC-EXAMPLE-BUCKET
      PolicyDocument:
        Statement:
          - Action:
              - 's3:GetObject'
            Effect: Deny
            Resource: '*'
            Principal: '*'
            Condition:
              StringLike:
                'aws:Referer':
                  - 'http://www.example.com/*'
                  - 'http://example.net/*'

Negative test num. 2 - json file

{
  "Resources": {
    "SampleBucketPolicy2": {
      "Type": "AWS::S3::BucketPolicy",
      "Properties": {
        "Bucket": {
          "Ref": "DOC-EXAMPLE-BUCKET"
        },
        "PolicyDocument": {
          "Statement": [
            {
              "Action": [
                "s3:GetObject"
              ],
              "Effect": "Deny",
              "Resource": "*",
              "Principal": "*",
              "Condition": {
                "StringLike": {
                  "aws:Referer": [
                    "http://www.example.com/*",
                    "http://example.net/*"
                  ]
                }
              }
            }
          ]
        }
      }
    }
  }
}