Default KMS Key Usage

• Query id: e52395b4-250b-4c60-81d5-2e58c1d37abc
• Query name: Default KMS Key Usage
• Platform: CloudFormation
• Severity: Medium
• Category: Encryption
• CWE: 311
• Risk score: 5.2
• URL: Github

Description

When StorageEncrypted is set to true, KmsKeyId should be defined, to avoid the use of the default KMS Key
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: >-
  AWS CloudFormation Sample Template
Parameters:
  DBUsername:
    NoEcho: 'true'
    Description: Username for MySQL database access
    Type: String
    MinLength: '1'
    MaxLength: '16'
    AllowedPattern: '[a-zA-Z][a-zA-Z0-9]*'
    ConstraintDescription: must begin with a letter and contain only alphanumeric characters.
  DBPassword:
    NoEcho: 'true'
    Description: Password MySQL database access
    Type: String
    MinLength: '8'
    MaxLength: '41'
    AllowedPattern: '[a-zA-Z0-9]*'
    ConstraintDescription: must contain only alphanumeric characters.
Resources:
  RDSCluster1:
    Type: 'AWS::RDS::DBCluster'
    Properties:
      MasterUsername: !Ref DBUsername
      MasterUserPassword: !Ref DBPassword
      DBClusterIdentifier: my-serverless-cluster
      Engine: aurora
      EngineVersion: 5.6.10a
      EngineMode: serverless
      ScalingConfiguration:
        AutoPause: true
        MinCapacity: 4
        MaxCapacity: 32
        SecondsUntilAutoPause: 1000
      StorageEncrypted: true

Positive test num. 2 - json file

{
  "Parameters": {
    "DBUsername": {
      "NoEcho": "true",
      "Description": "Username for MySQL database access",
      "Type": "String",
      "MinLength": "1",
      "MaxLength": "16",
      "AllowedPattern": "[a-zA-Z][a-zA-Z0-9]*",
      "ConstraintDescription": "must begin with a letter and contain only alphanumeric characters."
    },
    "DBPassword": {
      "Type": "String",
      "MinLength": "8",
      "MaxLength": "41",
      "AllowedPattern": "[a-zA-Z0-9]*",
      "ConstraintDescription": "must contain only alphanumeric characters.",
      "NoEcho": "true",
      "Description": "Password MySQL database access"
    }
  },
  "Resources": {
    "RDSCluster1": {
      "Type": "AWS::RDS::DBCluster",
      "Properties": {
        "DBClusterIdentifier": "my-serverless-cluster",
        "Engine": "aurora",
        "EngineVersion": "5.6.10a",
        "EngineMode": "serverless",
        "ScalingConfiguration": {
          "AutoPause": true,
          "MinCapacity": 4,
          "MaxCapacity": 32,
          "SecondsUntilAutoPause": 1000
        },
        "StorageEncrypted": true,
        "MasterUsername": "DBUsername",
        "MasterUserPassword": "DBPassword"
      }
    }
  },
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "AWS CloudFormation Sample Template"
}

Positive test num. 3 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: >-
  AWS CloudFormation Sample Template
Parameters:
  DBUsername:
    NoEcho: 'true'
    Description: Username for MySQL database access
    Type: String
    MinLength: '1'
    MaxLength: '16'
    AllowedPattern: '[a-zA-Z][a-zA-Z0-9]*'
    ConstraintDescription: must begin with a letter and contain only alphanumeric characters.
  DBPassword:
    NoEcho: 'true'
    Description: Password MySQL database access
    Type: String
    MinLength: '8'
    MaxLength: '41'
    AllowedPattern: '[a-zA-Z0-9]*'
    ConstraintDescription: must contain only alphanumeric characters.
Resources:
  RDSCluster1:
    Type: 'AWS::RDS::DBCluster'
    Properties:
      MasterUsername: !Ref DBUsername
      MasterUserPassword: !Ref DBPassword
      DBClusterIdentifier: my-serverless-cluster
      Engine: aurora
      EngineVersion: 5.6.10a
      EngineMode: serverless
      ScalingConfiguration:
        AutoPause: "true"
        MinCapacity: 4
        MaxCapacity: 32
        SecondsUntilAutoPause: 1000
      StorageEncrypted: "true"

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: RDS Storage Encrypted
Parameters:
  SourceDBInstanceIdentifier:
    Type: String
  DBInstanceType:
    Type: String
  SourceRegion:
    Type: String
Resources:
  MyKey:
    Type: "AWS::KMS::Key"
    Properties:
      KeyPolicy:
        Version: 2012-10-17
        Id: key-default-1
        Statement:
          - Sid: Enable IAM User Permissions
            Effect: Allow
            Principal:
              AWS: !Join
                - ""
                - - "arn:aws:iam::"
                  - !Ref "AWS::AccountId"
                  - ":root"
            Action: "kms:*"
            Resource: "*"
  MyDBSmall:
    Type: "AWS::RDS::DBInstance"
    Properties:
      DBInstanceClass: !Ref DBInstanceType
      SourceDBInstanceIdentifier: !Ref SourceDBInstanceIdentifier
      SourceRegion: !Ref SourceRegion
      KmsKeyId: !Ref MyKey
      StorageEncrypted: true

Negative test num. 2 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: >-
  AWS CloudFormation Sample Template
Parameters:
  DBUsername:
    NoEcho: 'true'
    Description: Username for MySQL database access
    Type: String
    MinLength: '1'
    MaxLength: '16'
    AllowedPattern: '[a-zA-Z][a-zA-Z0-9]*'
    ConstraintDescription: must begin with a letter and contain only alphanumeric characters.
  DBPassword:
    NoEcho: 'true'
    Description: Password MySQL database access
    Type: String
    MinLength: '8'
    MaxLength: '41'
    AllowedPattern: '[a-zA-Z0-9]*'
    ConstraintDescription: must contain only alphanumeric characters.
Resources:
  MyKey-0:
    Type: "AWS::KMS::Key"
    Properties:
      KeyPolicy:
        Version: 2012-10-17
        Id: key-default-1
        Statement:
          - Sid: Enable IAM User Permissions
            Effect: Allow
            Principal:
              AWS: !Join
                - ""
                - - "arn:aws:iam::"
                  - !Ref "AWS::AccountId"
                  - ":root"
            Action: "kms:*"
            Resource: "*"
  RDSCluster:
    Type: 'AWS::RDS::DBCluster'
    Properties:
      MasterUsername: !Ref DBUsername
      MasterUserPassword: !Ref DBPassword
      DBClusterIdentifier: my-serverless-cluster
      Engine: aurora
      EngineVersion: 5.6.10a
      EngineMode: serverless
      ScalingConfiguration:
        AutoPause: true
        MinCapacity: 4
        MaxCapacity: 32
        SecondsUntilAutoPause: 1000
      KmsKeyId: !Ref MyKey-0
      StorageEncrypted: true

Negative test num. 3 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "RDS Storage Encrypted",
  "Parameters": {
    "SourceDBInstanceIdentifier": {
      "Type": "String"
    },
    "DBInstanceType": {
      "Type": "String"
    },
    "SourceRegion": {
      "Type": "String"
    }
  },
  "Resources": {
    "MyKey": {
      "Type": "AWS::KMS::Key",
      "Properties": {
        "KeyPolicy": {
          "Version": "2012-10-17T00:00:00Z",
          "Id": "key-default-1",
          "Statement": [
            {
              "Principal": {
                "AWS": [
                  "",
                  [
                    "arn:aws:iam::",
                    "AWS::AccountId",
                    ":root"
                  ]
                ]
              },
              "Action": "kms:*",
              "Resource": "*",
              "Sid": "Enable IAM User Permissions",
              "Effect": "Allow"
            }
          ]
        }
      }
    },
    "MyDBSmall": {
      "Type": "AWS::RDS::DBInstance",
      "Properties": {
        "SourceRegion": "SourceRegion",
        "KmsKeyId": "MyKey",
        "StorageEncrypted": true,
        "DBInstanceClass": "DBInstanceType",
        "SourceDBInstanceIdentifier": "SourceDBInstanceIdentifier"
      }
    }
  }
}

Negative test num. 4 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: RDS Storage Encrypted
Parameters:
  SourceDBInstanceIdentifier:
    Type: String
  DBInstanceType:
    Type: String
  SourceRegion:
    Type: String
Resources:
  MyKey:
    Type: "AWS::KMS::Key"
    Properties:
      KeyPolicy:
        Version: 2012-10-17
        Id: key-default-1
        Statement:
          - Sid: Enable IAM User Permissions
            Effect: Allow
            Principal:
              AWS: !Join
                - ""
                - - "arn:aws:iam::"
                  - !Ref "AWS::AccountId"
                  - ":root"
            Action: "kms:*"
            Resource: "*"
  MyDBSmall:
    Type: "AWS::RDS::DBInstance"
    Properties:
      DBInstanceClass: !Ref DBInstanceType
      SourceDBInstanceIdentifier: !Ref SourceDBInstanceIdentifier
      SourceRegion: !Ref SourceRegion
      KmsKeyId: !Ref MyKey
      StorageEncrypted: "true"

Negative test num. 5 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "AWS CloudFormation Sample Template",
  "Parameters": {
    "DBUsername": {
      "MaxLength": "16",
      "AllowedPattern": "[a-zA-Z][a-zA-Z0-9]*",
      "ConstraintDescription": "must begin with a letter and contain only alphanumeric characters.",
      "NoEcho": "true",
      "Description": "Username for MySQL database access",
      "Type": "String",
      "MinLength": "1"
    },
    "DBPassword": {
      "Type": "String",
      "MinLength": "8",
      "MaxLength": "41",
      "AllowedPattern": "[a-zA-Z0-9]*",
      "ConstraintDescription": "must contain only alphanumeric characters.",
      "NoEcho": "true",
      "Description": "Password MySQL database access"
    }
  },
  "Resources": {
    "MyKey-0": {
      "Type": "AWS::KMS::Key",
      "Properties": {
        "KeyPolicy": {
          "Version": "2012-10-17T00:00:00Z",
          "Id": "key-default-1",
          "Statement": [
            {
              "Sid": "Enable IAM User Permissions",
              "Effect": "Allow",
              "Principal": {
                "AWS": [
                  "",
                  [
                    "arn:aws:iam::",
                    "AWS::AccountId",
                    ":root"
                  ]
                ]
              },
              "Action": "kms:*",
              "Resource": "*"
            }
          ]
        }
      }
    },
    "RDSCluster": {
      "Type": "AWS::RDS::DBCluster",
      "Properties": {
        "StorageEncrypted": true,
        "MasterUsername": "DBUsername",
        "DBClusterIdentifier": "my-serverless-cluster",
        "ScalingConfiguration": {
          "MinCapacity": 4,
          "MaxCapacity": 32,
          "SecondsUntilAutoPause": 1000,
          "AutoPause": true
        },
        "EngineMode": "serverless",
        "KmsKeyId": "MyKey-0",
        "MasterUserPassword": "DBPassword",
        "Engine": "aurora",
        "EngineVersion": "5.6.10a"
      }
    }
  }
}