Instance with no VPC

Docs > Datadog Security > Code Security > Infrastructure as Code (IaC) Security > IaC Security Rules > Instance with no VPC

Metadata

Id: cloudformation-aws-instance-with-no-vpc

Provider: AWS

Platform: CloudFormation

Severity: Low

Category: Insecure Configurations

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Provider Reference

Description

EC2 instances must be launched into VPC subnets so they are subject to VPC network controls (routing and security groups) and are not placed in undefined network contexts that can increase exposure risk.

In AWS CloudFormation:

AWS::EC2::Instance resources must define Properties.NetworkInterfaces.
Each NetworkInterfaces[].SubnetId that references an AWS::EC2::Subnet resource must point to a subnet that defines Properties.VpcId.

This rule flags AWS::EC2::Instance resources missing NetworkInterfaces and flags subnet resources referenced by SubnetId when the referenced AWS::EC2::Subnet lacks a VpcId property. If you supply SubnetId as a literal ID or parameter instead of a template resource reference, ensure that the referenced subnet ID belongs to a VPC. The check validates VPC association only when SubnetId points to a template resource.

Secure example with a subnet declaring VpcId and an instance using a network interface that references it:

MySubnet:
  Type: AWS::EC2::Subnet
  Properties:
    VpcId: !Ref MyVPC
    CidrBlock: 10.0.1.0/24

MyInstance:
  Type: AWS::EC2::Instance
  Properties:
    NetworkInterfaces:
      - DeviceIndex: 0
        SubnetId: !Ref MySubnet
        AssociatePublicIpAddress: false
        GroupSet:
          - !Ref MySecurityGroup

Compliant Code Examples

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.1.0.0/16
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
          - Key: Name
            Value:  !Join ['', [!Ref "AWS::StackName", "-VPC" ]]
  InternetGateway:
    Type: AWS::EC2::InternetGateway
    DependsOn: VPC
  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref VPC
      InternetGatewayId: !Ref InternetGateway
  PublicSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.1.10.0/24
      AvailabilityZone: !Select [ 0, !GetAZs ]    # Obtenha o primeiro AZ na lista
      Tags:
          - Key: Name
            Value: !Sub ${AWS::StackName}-Public-A
  Ec2Instance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: 'some-ec2-image'
      Fn::FindInMap:
            - "RegionMap"
            - Ref: "AWS::Region"
            - "AMI"
      KeyName: 'some-rsa-key'
      Ref: "KeyName"
      NetworkInterfaces:
        -   AssociatePublicIpAddress: "true"
            DeviceIndex: 0
            SubnetId: !Ref PublicSubnetA

Non-Compliant Code Examples

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: 10.1.0.0/16
      EnableDnsSupport: true
      EnableDnsHostnames: true
      Tags:
          - Key: Name
            Value:  !Join ['', [!Ref "AWS::StackName", "-VPC" ]]
  InternetGateway:
    Type: AWS::EC2::InternetGateway
    DependsOn: VPC
  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref VPC
      InternetGatewayId: !Ref InternetGateway
  PublicSubnetA:
    Type: AWS::EC2::Subnet
    Properties:
      CidrBlock: 10.1.10.0/24
      AvailabilityZone: !Select [ 0, !GetAZs ]    # Obtenha o primeiro AZ na lista
      Tags:
          - Key: Name
            Value: !Sub ${AWS::StackName}-Public-A
  Ec2Instance-01:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: "some-ec2-image"
      Fn::FindInMap:
            - "RegionMap"
            - Ref: "AWS::Region"
            - "AMI"
      KeyName: "some-rsa-key"
      Ref: "KeyName"
      NetworkInterfaces:
        -   AssociatePublicIpAddress: "true"
            DeviceIndex: 0
            SubnetId: !Ref PublicSubnetA

Resources:
  Ec2Instance-02:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: "some-ec2-image"
      Fn::FindInMap:
            - "RegionMap"
            - Ref: "AWS::Region"
            - "AMI"
      KeyName: "some-rsa-key"
      Ref: "KeyName"