AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Security Hub Updater

Parameters:
  Path:
    Type: String
    Default: "/"
    Description: Path for IAM Role
  MemberIAMRoleName:
    Type: String
    Default: "securityhub-UpdateControl-role"
    Description: Name of IAM Role in member account
  MemberIAMRolePath:
    Type: String
    Default: "/"
    Description: Path of IAM Role in member account
  Schedule:
    Type: String
    Default: "rate(1 day)"
    Description: The scheduling expression that determines when and how often the SecurityHubUpdater runs.
  EventTriggerState:
    Type: String
    Default: "DISABLED"
    AllowedValues: ["ENABLED", "DISABLED"]
    Description: The state of the SecurityHubUpdateEvent rule monitoring Security Hub control updates and triggering the state machine
  
  # TODO - Subscriptions: If you need more e-mail subscriptions, add another parameter. Also, add another condition in the "Conditions" section and adapt the list of subscriptions in the StateMachineFailureSNSTopic resource accordingly.
  NotificationEmail1:
    Type: String
    Default: ""
    Description: Optional - E-mail address to receive notification if the state machine fails.
  NotificationEmail2:
    Type: String
    Default: ""
    Description: Optional - E-mail address to receive notification if the state machine fails.
  NotificationEmail3:
    Type: String
    Default: ""
    Description: Optional - E-mail address to receive notification if the state machine fails.

Conditions:
  # TODO - Subscriptions: Add another "!Not [!Equals [...]]" Condition into the list for each additional email parameter added.
  NotificationEmail1Exists: !Not [!Equals [!Ref NotificationEmail1, ""]]
  NotificationEmail2Exists: !Not [!Equals [!Ref NotificationEmail2, ""]]
  NotificationEmail3Exists: !Not [!Equals [!Ref NotificationEmail3, ""]]

Resources:

  AccountExceptions:
    Type: AWS::DynamoDB::Table
    Properties:
      AttributeDefinitions:
        -
          AttributeName: "ControlId"
          AttributeType: "S"
        # -
        #   AttributeName: "Disabled"
        #   AttributeType: "S"
        # -
        #   AttributeName: "Eisabled"
        #   AttributeType: "S"
      BillingMode: "PAY_PER_REQUEST"
      KeySchema:
        -
          AttributeName: "ControlId"
          KeyType: "HASH"
      # ProvisionedThroughput:
      #   ReadCapacityUnits: 5
      #   WriteCapacityUnits: 5

  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      Path: !Ref Path
      AssumeRolePolicyDocument:
        Statement:
        - Action:
          - sts:AssumeRole
          Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
        Version: '2012-10-17'
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
      - PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action: sts:AssumeRole
              Resource:
                - !Sub "arn:aws:iam::*:role${MemberIAMRolePath}${MemberIAMRoleName}"
            - Effect: Allow
              Action:
                - securityhub:Get*
                - securityhub:List*
                - securityhub:Describe*
                - organizations:ListAccounts
              Resource: "*"
            - Effect: Allow
              Action:
                - dynamodb:Query
                - dynamodb:Scan
              Resource: !GetAtt AccountExceptions.Arn
        PolicyName: SecurityHubUpdateStandardsControlPolicyForLambda

  CheckResult:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: ./src/CheckResult
      Description: Checks results of UpdateMember executions
      Handler: index.lambda_handler
      Role:
        Fn::GetAtt:
        - LambdaExecutionRole
        - Arn
      Runtime: python3.8
      Timeout: 300

  GetMembers:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: ./src/GetMembers
      Description: Get list of member accounts from SecurityHub
      Handler: index.lambda_handler
      Role:
        Fn::GetAtt:
        - LambdaExecutionRole
        - Arn
      Runtime: python3.8
      Timeout: 300
      Environment:
        Variables:
          Schedule: !Ref Schedule
          DynamoDB: !Ref AccountExceptions

  UpdateMember:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: ./src/UpdateMember
      Description: Update the state of SecurityHub findings in all member accounts
      Handler: index.lambda_handler
      Role:
        Fn::GetAtt:
        - LambdaExecutionRole
        - Arn
      Runtime: python3.8
      Timeout: 900
      Environment:
        Variables:
          MemberRole: !Sub "arn:aws:iam::<accountId>:role${MemberIAMRolePath}${MemberIAMRoleName}"

  SecurityHubMemberUpdateStateMachineRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Statement:
          - Action:
              - sts:AssumeRole
            Effect: Allow
            Principal:
              Service:
                - states.amazonaws.com
        Version: "2012-10-17"
      Policies:
        - PolicyName: InvokeLambdaPolicyForStateMachines
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Sid: InvokeLambdas
                Effect: Allow
                Action:
                  - "lambda:InvokeFunction"
                  - "lambda:Get*"
                  - "lambda:List*"
                Resource:
                  - !GetAtt UpdateMember.Arn
                  - !GetAtt GetMembers.Arn
                  - !GetAtt CheckResult.Arn
              - Sid: PublishSNS
                Effect: Allow
                Action:
                  - "sns:Publish"
                Resource: !Ref StateMachineFailureSNSTopic

  SecurityHubMemberUpdate:
    Type: AWS::Serverless::StateMachine
    Properties:
      Role: !GetAtt SecurityHubMemberUpdateStateMachineRole.Arn
      DefinitionUri: ./stateMachine.json
      DefinitionSubstitutions:
        UpdateMember: !GetAtt UpdateMember.Arn
        GetMembers: !GetAtt GetMembers.Arn
        CheckResult: !GetAtt CheckResult.Arn
        StateMachineFailureSNSTopic: !Ref StateMachineFailureSNSTopic
      Events:
        Scheduled:
          Type: Schedule
          Properties:
            Input: '{"scheduled": "True"}'
            Schedule: !Ref Schedule

  SecurityHubUpdatedEvent:
    Type: AWS::Events::Rule
    Properties:
      Description: This rule monitors Security Hub and executes the state machine if a Security Hub control was updated
      State: !Ref EventTriggerState
      RoleArn: !GetAtt SecurityHubUpdatedEventRole.Arn
      Targets:
      - Arn: !Ref SecurityHubMemberUpdate
        Id: SecurityHubUpdaterStateMachine
        RoleArn: !GetAtt SecurityHubUpdatedEventRole.Arn
      EventPattern:
        source:
          - aws.securityhub
        detail-type:
          - AWS API Call via CloudTrail
        detail:
          eventSource:
            - securityhub.amazonaws.com
          eventName:
            - UpdateStandardsControl
            - BatchDisableStandards
            - BatchEnableStandards

  SecurityHubUpdatedEventRole:
    Type: AWS::IAM::Role
    Properties:
      Path: !Ref Path
      AssumeRolePolicyDocument:
        Statement:
        - Action:
          - sts:AssumeRole
          Effect: Allow
          Principal:
            Service:
            - events.amazonaws.com
        Version: '2012-10-17'
      Policies:
      - PolicyDocument:
          Version: '2012-10-17'
          Statement:
            - Effect: Allow
              Action:
                - states:StartExecution
              Resource: !Ref SecurityHubMemberUpdate
        PolicyName: StartStateMachine

  StateMachineFailureSNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      Subscription:
      # TODO - Subscriptions: Add another "!If" statement into the list for each additional email parameter added.
        - !If
          - NotificationEmail1Exists
          - 
            Endpoint: !Ref NotificationEmail1
            Protocol: email
          - !Ref AWS::NoValue
        - !If
          - NotificationEmail2Exists
          - 
            Endpoint: !Ref NotificationEmail2
            Protocol: email
          - !Ref AWS::NoValue
        - !If
          - NotificationEmail3Exists
          - 
            Endpoint: !Ref NotificationEmail3
            Protocol: email
          - !Ref AWS::NoValue

  StateMachineFailureSNSTopicPolicyEventRule:
    Type: "AWS::SNS::TopicPolicy"
    Properties:
      PolicyDocument:
        Statement:
          - Sid: PublishMessage
            Effect: "Allow"
            Principal:
              AWS: "*"
            Action:
              - "sns:Publish"
            Resource: !Ref StateMachineFailureSNSTopic
            Condition:
              StringEquals:
                AWS:PrincipalArn: !GetAtt SecurityHubMemberUpdateStateMachineRole.Arn
      Topics:
        - !Ref StateMachineFailureSNSTopic

Outputs:
  StateMachineArn:
    Value: !Ref SecurityHubMemberUpdate
  CheckResultLambda:
    Value: !Ref CheckResult
  GetMembersLambda:
    Value: !Ref GetMembers
  UpdateMemberLambda:
    Value: !Ref UpdateMember
  SNSTopic:
    Value: !Ref StateMachineFailureSNSTopic
  AccountExceptionsDynamoDBTableName:
    Value: !Ref AccountExceptions