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name: aws-cloudformation-security description: Provides AWS CloudFormation patterns for security infrastructure including KMS encryption, Secrets Manager, IAM security, VPC security, ACM certificates, parameter security, outputs, and secure cross-stack references. Use when implementing security best practices, encrypting data, managing secrets, applying least privilege IAM policies, securing VPC configurations, managing TLS/SSL certificates, and implementing defense in depth strategies. allowed-tools: Read, Write, Bash

AWS CloudFormation Security Infrastructure

Overview

Create production-ready security infrastructure using AWS CloudFormation templates. This skill covers KMS encryption, Secrets Manager, IAM security with least privilege, VPC security configurations, ACM certificates, parameter security, secure outputs, cross-stack references, CloudWatch Logs encryption, defense in depth strategies, and security best practices.

When to Use

• Implementing KMS encryption at rest and in transit
• Managing secrets with Secrets Manager and automatic rotation
• Applying IAM least privilege policies and permission boundaries
• Securing VPC with security groups, NACLs, and VPC endpoints
• Managing TLS/SSL certificates with ACM
• Encrypting CloudWatch Logs and S3 buckets
• Creating secure cross-stack references and outputs

Instructions

Follow these steps to create security infrastructure with CloudFormation:

1. Define KMS Encryption Keys

Create customer-managed keys for encryption:

Resources:
  EncryptionKey:
    Type: AWS::KMS::Key
    Properties:
      Description: Customer-managed key for data encryption
      KeyPolicy:
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action:
              - kms:Decrypt
              - kms:GenerateDataKey
            Resource: "*"
          - Effect: Allow
            Principal:
              AWS: !Sub "arn:aws:iam::${AWS::AccountId}:root"
            Action:
              - kms:*
            Resource: "*"

  KeyAlias:
    Type: AWS::KMS::Alias
    Properties:
      AliasName: !Sub "${AWS::StackName}/encryption-key"
      TargetKeyId: !Ref EncryptionKey

Validate: aws kms get-key-policy --key-id <key-id> --output text

2. Manage Secrets with Secrets Manager

Store and retrieve sensitive data securely:

Resources:
  DatabaseSecret:
    Type: AWS::SecretsManager::Secret
    Properties:
      Name: !Sub "${AWS::StackName}/database"
      Description: Database credentials
      SecretString: !Sub |
        {
          "username": "admin",
          "password": "${DatabasePassword}",
          "engine": "mysql",
          "host": "${DatabaseEndpoint}",
          "port": 3306
        }
      KmsKeyId: !Ref EncryptionKey

  SecretRotationSchedule:
    Type: AWS::SecretsManager::RotationSchedule
    Properties:
      SecretId: !Ref DatabaseSecret
      RotationLambdaARN: !Ref RotationLambda.Arn
      RotationRules:
        AutomaticallyAfterDays: 30

Validate: aws secretsmanager describe-secret --secret-id <secret-name>

3. Apply IAM Least Privilege

Create roles and policies with minimal required permissions:

Resources:
  ExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Policies:
        - PolicyName: SpecificPermissions
          PolicyDocument:
            Version: "2012-10-17"
            Statement:
              - Effect: Allow
                Action:
                  - s3:GetObject
                Resource: !Sub "${DataBucket.Arn}/*"

Validate: aws iam simulate-principal-policy --policy-source-arn <role-arn> --action-names s3:GetObject --resource-arns <bucket-arn>

4. Secure VPC Configuration

Implement network security with security groups and NACLs:

Resources:
  ApplicationSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Application security group
      VpcId: !Ref VPC
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 443
          ToPort: 443
          SourceSecurityGroupId: !Ref LoadBalancerSecurityGroup
      SecurityGroupEgress:
        - IpProtocol: -1
          CidrIp: 0.0.0.0/0

  ApplicationNACL:
    Type: AWS::EC2::NetworkAcl
    Properties:
      VpcId: !Ref VPC

  NACLEntry:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
      NetworkAclId: !Ref ApplicationNACL
      RuleNumber: 100
      Protocol: "6"
      RuleAction: allow
      Egress: false
      CidrBlock: 0.0.0.0/0
      PortRange:
        From: 443
        To: 443

Validate: aws ec2 describe-security-groups --group-ids <sg-id> --query 'SecurityGroups[0].IpPermissions'

5. Request ACM Certificates

Manage TLS/SSL certificates for secure communication:

Resources:
  Certificate:
    Type: AWS::ACM::Certificate
    Properties:
      DomainName: !Ref DomainName
      SubjectAlternativeNames:
        - !Sub "www.${DomainName}"
        - !Sub "api.${DomainName}"
      DomainValidationOptions:
        - DomainName: !Ref DomainName
          ValidationDomain: !Ref DomainName
      Tags:
        - Key: Environment
          Value: !Ref Environment

  # DNS validation record
  DnsValidationRecord:
    Type: AWS::Route53::RecordSet
    Properties:
      HostedZoneName: !Ref HostedZone
      Name: !Sub "_${DomainName}."
      Type: CNAME
      TTL: 300
      ResourceRecords:
        - !Ref Certificate

Validate: aws acm describe-certificate --certificate-arn <arn> --query 'Certificate.Status'

6. Implement Secure Parameters

Use SecureString for sensitive parameter values:

Resources:
  DatabasePasswordParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: !Sub "/${AWS::StackName}/database/password"
      Type: SecureString
      Value: !Ref DatabasePassword
      Description: Database master password
      KmsKeyId: !Ref EncryptionKey

  # Reference in other resources
  DatabaseInstance:
    Type: AWS::RDS::DBInstance
    Properties:
      MasterUsername: admin
      MasterUserPassword: !Ref DatabasePasswordParameter

Validate: aws ssm get-parameter --name <param-name> --with-decryption --query 'Parameter.Type'

7. Create Secure Outputs

Export only non-sensitive values from stacks:

Outputs:
  # Safe to export
  KMSKeyArn:
    Description: KMS Key ARN for encryption
    Value: !GetAtt EncryptionKey.Arn
    Export:
      Name: !Sub "${AWS::StackName}-KMSKeyArn"

  SecretArn:
    Description: Secret ARN (not the secret value)
    Value: !Ref DatabaseSecret
    Export:
      Name: !Sub "${AWS::StackName}-SecretArn"

  # DO NOT export sensitive data
  # Incorrect:
  # SecretValue:
  #   Value: !GetAtt DatabaseSecret.SecretString

Validate: aws cloudformation list-exports --query "Exports[?Name=='<stack-name>-KMSKeyArn']"

8. Encrypt CloudWatch Logs

Enable encryption for log groups:

Resources:
  EncryptedLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Sub "/aws/applications/${ApplicationName}"
      RetentionInDays: 30
      KmsKeyId: !Ref EncryptionKey

Validate: aws logs describe-log-groups --log-group-name-prefix <prefix> --query 'logGroups[0].kmsKeyId'

Best Practices

• KMS: Use separate keys per data classification; enable annual key rotation; use customer-managed keys for compliance
• Secrets: Rotate automatically (30 days for databases); never store secrets in plain text; use IAM policies for access control
• IAM: Apply least privilege; use roles not access keys; enable MFA; implement permission boundaries
• Network: Prefer security groups over NACLs; use VPC endpoints; restrict by specific CIDR ranges
• Certificates: Use ACM for automatic renewal; DNS validation is faster than email
• Encryption: Encrypt at rest and in transit; TLS 1.2+ required; use SSE-KMS for S3

Examples

Complete KMS and Secrets Stack

Resources:
  # KMS Key with proper policy
  AppKey:
    Type: AWS::KMS::Key
    Properties:
      KeyPolicy:
        Statement:
          - Effect: Allow
            Principal:
              AWS: !Sub "arn:aws:iam::${AWS::AccountId}:root"
            Action: kms:*
            Resource: "*"
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action:
              - kms:Decrypt
              - kms:GenerateDataKey
            Resource: "*"

  # Secrets Manager with rotation
  DbSecret:
    Type: AWS::SecretsManager::Secret
    Properties:
      SecretString: !Sub '{"password":"${DbPassword}"}'
      KmsKeyId: !Ref AppKey
      RotationRules:
        AutomaticallyAfterDays: 30

IAM Least Privilege Role

Resources:
  LambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      Policies:
        - PolicyName: AccessPolicy
          PolicyDocument:
            Statement:
              - Effect: Allow
                Action: s3:GetObject
                Resource: !Sub "${Bucket.Arn}/*"

For comprehensive examples with VPC security groups, ACM certificates, and complete encrypted infrastructure stacks, see examples.md.

Constraints and Warnings

Resource Limits

• Security groups: max 60 inbound + 60 outbound rules
• NACLs: max 20 inbound + 20 outbound rules per subnet
• VPCs: max 5 per region (soft limit)
• Key rotation: annual for KMS customer-managed keys

Security Constraints

• NACLs are stateless: return traffic must be explicitly allowed
• Default security groups cannot be deleted
• Security group references cannot span VPC peering (use CIDR)
• Cross-account access requires both IAM and resource policies

Operational Warnings

• Secrets rotation requires Lambda function with proper IAM permissions
• KMS key deletion requires pending window (7-30 days)
• ACM certificates need DNS validation before issuance
• VPC CIDR blocks cannot overlap with peered VPCs

For detailed constraints including cost considerations and quota management, see constraints.md.

References

For detailed implementation guidance, see:

• examples.md - Complete KMS stacks, Secrets Manager with rotation, IAM least privilege roles, VPC security groups, ACM certificates, and encrypted infrastructure
• constraints.md - Resource limits, security constraints, operational constraints, network constraints, cost considerations, and access control constraints