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Wildcard in ACM certificate domain name

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Metadata

Id: cloudformation-aws-wildcard-in-acm-certificate-domain-name

Provider: AWS

Platform: CloudFormation

Severity: Low

Category: Insecure Configurations

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Description

Using a bare wildcard (*) as an ACM certificate DomainName creates overly broad trust and can enable certificate issuance or use that is not tied to a specific domain. This increases the risk of impersonation and unauthorized TLS termination.

For AWS::CertificateManager::Certificate resources, Properties.DomainName must be a valid domain or a properly scoped wildcard subdomain (for example, example.com or *.example.com) and must not be the single character *. Resources where DomainName is exactly * will be flagged. Use explicit hostnames or scoped wildcard names and, if you need multiple names, list them in SubjectAlternativeNames rather than using a universal wildcard.

Secure configuration example:

MyCertificate:
  Type: AWS::CertificateManager::Certificate
  Properties:
    DomainName: www.example.com
    ValidationMethod: DNS

Compliant Code Examples

AWSTemplateFormatVersion: '2010-09-09'
Parameters:
  DomainName:
    Description: "Domain for which you are requesting a cert"
    Type: String
    Default: example.com #Put your own domain name here
  HostedZoneId:
    Description: "hosted zone id in which CNAME record for the validation needs to be added"
    Type: String
    Default: XYZABCDERYH #Put the hosted zone id in which CNAME record for the validation needs to be added

Resources:
  Certificate:
    Type: AWS::CertificateManager::Certificate
    Properties:
      DomainName: CMDomain
      DomainValidationOptions:
        - DomainName: !Ref DomainName
          HostedZoneId: !Ref HostedZoneId
      ValidationMethod: 'DNS'

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "DomainName": {
      "Type": "String",
      "Default": "example.com",
      "Description": "Domain for which you are requesting a cert"
    },
    "HostedZoneId": {
      "Description": "hosted zone id in which CNAME record for the validation needs to be added",
      "Type": "String",
      "Default": "XYZABCDERYH"
    }
  },
  "Resources": {
    "Certificate": {
      "Type": "AWS::CertificateManager::Certificate",
      "Properties": {
        "DomainName": "CMDomain",
        "DomainValidationOptions": [
          {
            "HostedZoneId": "HostedZoneId",
            "DomainName": "DomainName"
          }
        ],
        "ValidationMethod": "DNS"
      }
    }
  }
}

Non-Compliant Code Examples

AWSTemplateFormatVersion: '2010-09-09'
Parameters:
  DomainName:
    Description: "Domain for which you are requesting a cert"
    Type: String
    Default: example.com #Put your own domain name here
  HostedZoneId:
    Description: "hosted zone id in which CNAME record for the validation needs to be added"
    Type: String
    Default: XYZABCDERYH #Put the hosted zone id in which CNAME record for the validation needs to be added

Resources:
  Certificate:
    Type: AWS::CertificateManager::Certificate
    Properties:
      DomainName: "*"
      DomainValidationOptions:
        - DomainName: !Ref DomainName
          HostedZoneId: !Ref HostedZoneId
      ValidationMethod: 'DNS'

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Parameters": {
    "HostedZoneId": {
      "Type": "String",
      "Default": "XYZABCDERYH",
      "Description": "hosted zone id in which CNAME record for the validation needs to be added"
    },
    "DomainName": {
      "Description": "Domain for which you are requesting a cert",
      "Type": "String",
      "Default": "example.com"
    }
  },
  "Resources": {
    "Certificate": {
      "Type": "AWS::CertificateManager::Certificate",
      "Properties": {
        "DomainName": "*",
        "DomainValidationOptions": [
          {
            "DomainName": "DomainName",
            "HostedZoneId": "HostedZoneId"
          }
        ],
        "ValidationMethod": "DNS"
      }
    }
  }
}