---
title: Security groups without VPC attached
description: Datadog, the leading service for cloud-scale monitoring.
breadcrumbs: >-
  Docs > Datadog Security > Code Security > Infrastructure as Code (IaC)
  Security > IaC Security Rules > Security groups without VPC attached
---

# Security groups without VPC attached

{% callout %}
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## Metadata{% #metadata %}

**Id:** `cloudformation-aws-security-groups-without-vpc-attached` 

**Provider:** AWS

**Platform:** CloudFormation

**Severity:** Low

**Category:** Networking and Firewall

#### Learn More{% #learn-more %}

- [Provider Reference](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-security-group.html)

### Description{% #description %}

Security groups must be associated with a specific VPC to ensure network isolation and to allow enforcement of VPC-level controls. A security group without a `VpcId` may end up outside the intended VPC (or require EC2-Classic), which prevents proper subnet scoping, VPC flow logging, and other VPC security controls and can lead to unintended exposure.

For `AWS::EC2::SecurityGroup` resources, `Properties.VpcId` must be defined (for example, `!Ref MyVPC` or an explicit VPC ID). This rule flags security groups where `Properties.VpcId` is undefined and the group is not the default group (`GroupName != "default"`).

Secure example with `VpcId` set:

```yaml
MySecurityGroup:
  Type: AWS::EC2::SecurityGroup
  Properties:
    GroupDescription: Allow HTTP
    VpcId: !Ref MyVPC
    SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 80
        ToPort: 80
        CidrIp: 10.0.0.0/16
```

## Compliant Code Examples{% #compliant-code-examples %}

```yaml
Parameters:
  KeyName:
    Description: The EC2 Key Pair to allow SSH access to the instance
    Type: 'AWS::EC2::KeyPair::KeyName'
Resources:
  Ec2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      SecurityGroups:
        - !Ref InstanceSecurityGroup
        - MyExistingSecurityGroup
      KeyName: !Ref KeyName
      ImageId: ami-7a11e213
  InstanceSecurityGroup:
    Type: 'AWS::EC2::SecurityGroup'
    Properties:
      GroupName: My Group Name
      GroupDescription: Enable SSH access via port 22
      VpcId:
        Ref: myVPC
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: '22'
          ToPort: '22'
          CidrIp: 0.0.0.0/0
```

```json
{
  "Resources": {
    "Ec2Instance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "SecurityGroups": [
          "InstanceSecurityGroup",
          "MyExistingSecurityGroup"
        ],
        "KeyName": "KeyName",
        "ImageId": "ami-7a11e213"
      }
    },
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "SecurityGroupIngress": [
          {
            "IpProtocol": "tcp",
            "FromPort": "22",
            "ToPort": "22",
            "CidrIp": "0.0.0.0/0"
          }
        ],
        "GroupName": "My Group Name",
        "GroupDescription": "Enable SSH access via port 22",
        "VpcId": {
          "Ref": "myVPC"
        }
      }
    }
  },
  "Parameters": {
    "KeyName": {
      "Description": "The EC2 Key Pair to allow SSH access to the instance",
      "Type": "AWS::EC2::KeyPair::KeyName"
    }
  }
}
```

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```yaml
Parameters:
  KeyName:
    Description: The EC2 Key Pair to allow SSH access to the instance
    Type: 'AWS::EC2::KeyPair::KeyName'
Resources:
  Ec2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      SecurityGroups:
        - !Ref InstanceSecurityGroup
        - MyExistingSecurityGroup
      KeyName: !Ref KeyName
      ImageId: ami-7a11e213
  InstanceSecurityGroup:
    Type: 'AWS::EC2::SecurityGroup'
    Properties:
      GroupName: My Group Name
      GroupDescription: Enable SSH access via port 22
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: '22'
          ToPort: '22'
          CidrIp: 0.0.0.0/0
```

```json
{
  "Parameters": {
    "KeyName": {
      "Description": "The EC2 Key Pair to allow SSH access to the instance",
      "Type": "AWS::EC2::KeyPair::KeyName"
    }
  },
  "Resources": {
    "Ec2Instance": {
      "Properties": {
        "SecurityGroups": [
          "InstanceSecurityGroup",
          "MyExistingSecurityGroup"
        ],
        "KeyName": "KeyName",
        "ImageId": "ami-7a11e213"
      },
      "Type": "AWS::EC2::Instance"
    },
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "GroupName": "My Group Name",
        "GroupDescription": "Enable SSH access via port 22",
        "SecurityGroupIngress": [
          {
            "IpProtocol": "tcp",
            "FromPort": "22",
            "ToPort": "22",
            "CidrIp": "0.0.0.0/0"
          }
        ]
      }
    }
  }
}
```