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SNS topic without KmsMasterKeyId

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Metadata

Id: cloudformation-aws-sns-topic-without-kms-master-key-id

Provider: AWS

Platform: CloudFormation

Severity: Low

Category: Secret Management

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Description

SNS topics should use a customer-managed AWS KMS key for server-side encryption to protect published messages at rest and to enable controllable key access, rotation, and auditability.

In CloudFormation, AWS::SNS::Topic resources must define Properties.KmsMasterKeyId and set it to a KMS key identifier (key ARN, key ID, alias such as alias/your-alias, or a Ref/Fn::GetAtt to an AWS::KMS::Key). Resources missing this property will be flagged. When KmsMasterKeyId is undefined, SNS falls back to the AWS-managed key (aws/sns), which you cannot fully manage via custom key policies or rotation and which may not meet compliance or cross-account access requirements.

Secure configuration example (CloudFormation YAML):

MyKey:
  Type: AWS::KMS::Key
  Properties:
    Description: "CMK for SNS topic encryption"

MyTopic:
  Type: AWS::SNS::Topic
  Properties:
    TopicName: my-topic
    KmsMasterKeyId: !Ref MyKey

Compliant Code Examples

AWSTemplateFormatVersion: 2010-09-09
Resources:
  MySNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      Subscription:
        - Endpoint:
            Fn::GetAtt:
              - "MyQueue1"
              - "Arn"
          Protocol: "sqs"
        - Endpoint:
            Fn::GetAtt:
              - "MyQueue2"
              - "Arn"
          Protocol: "sqs"
      TopicName: "SampleTopic"
      KmsMasterKeyId: "kmsMasterKeyId"

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Resources": {
    "MySNSTopic": {
      "Type": "AWS::SNS::Topic",
      "Properties": {
        "Subscription": [
          {
            "Endpoint": {
              "Fn::GetAtt": [
                "MyQueue1",
                "Arn"
              ]
            },
            "Protocol": "sqs"
          },
          {
            "Endpoint": {
              "Fn::GetAtt": [
                "MyQueue2",
                "Arn"
              ]
            },
            "Protocol": "sqs"
          }
        ],
        "TopicName": "SampleTopic",
        "KmsMasterKeyId": "kmsMasterKeyId"
      }
    }
  }
}

Non-Compliant Code Examples

AWSTemplateFormatVersion: 2010-09-09
Resources:
  MySNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      Subscription:
        - Endpoint:
            Fn::GetAtt:
              - "MyQueue1"
              - "Arn"
          Protocol: "sqs"
        - Endpoint:
            Fn::GetAtt:
              - "MyQueue2"
              - "Arn"
          Protocol: "sqs"
      TopicName: "SampleTopic"

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Resources": {
    "MySNSTopic": {
      "Type": "AWS::SNS::Topic",
      "Properties": {
        "Subscription": [
          {
            "Endpoint": {
              "Fn::GetAtt": [
                "MyQueue1",
                "Arn"
              ]
            },
            "Protocol": "sqs"
          },
          {
            "Endpoint": {
              "Fn::GetAtt": [
                "MyQueue2",
                "Arn"
              ]
            },
            "Protocol": "sqs"
          }
        ],
        "TopicName": "SampleTopic"
      }
    }
  }
}