VPC Default Security Group Has Rules

What this rule checks

Detects standalone security group rules attached to a VPC default security group (GroupId referencing Fn::GetAtt DefaultSecurityGroup). CIS requires the default group to have no rules.

How to fix it

1. 1Attach rules to a purpose-built security group instead of the VPC default group
2. 2In CDK, enable restrictDefaultSecurityGroup: true on the Vpc so the default group has no rules

import { App, Stack } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as ec2 from 'aws-cdk-lib/aws-ec2';

const vpc = new ec2.CfnVPC(this, 'Vpc', { cidrBlock: '10.0.0.0/16' });
// FLAGGED: a standalone ingress rule targets the VPC's real default SG.
new ec2.CfnSecurityGroupIngress(this, 'DefaultSgIngress', {
  groupId: vpc.attrDefaultSecurityGroup,
  ipProtocol: 'tcp',
  fromPort: 443,
  toPort: 443,
  cidrIp: '0.0.0.0/0',
});

import { App, Stack } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as ec2 from 'aws-cdk-lib/aws-ec2';

const vpc = new ec2.CfnVPC(this, 'Vpc', { cidrBlock: '10.0.0.0/16' });
// FIXED: the default group stays untouched; a purpose-built SG carries rules.
const webSg = new ec2.CfnSecurityGroup(this, 'WebSg', {
  vpcId: vpc.ref,
  groupDescription: 'web tier',
});
new ec2.CfnSecurityGroupIngress(this, 'WebIngress', {
  groupId: webSg.attrGroupId,
  ipProtocol: 'tcp',
  fromPort: 443,
  toPort: 443,
  cidrIp: '0.0.0.0/0',
});

CDK Insights pinpoints the exact file and line in your CDK source for every finding, so you can jump straight to the fix.

Affected resource types

Intentional? Suppress this finding

Sometimes a flag is deliberate - a genuinely public endpoint, say. You can dismiss vpc-default-security-group-rules-present and the reason is kept in the report, not silently hidden.

In .cdk-insights.json:

{
  "ignoreRules": [
    { "id": "vpc-default-security-group-rules-present", "reason": "Why this is intentional" }
  ]
}

Or inline in your CDK code:

Validations.of(scope).acknowledge({
  id: 'cdk-insights::vpc-default-security-group-rules-present',
  reason: 'Why this is intentional',
});

Use the rule ID vpc-default-security-group-rules-present shown above - not the CDK-* ID from SARIF / GitHub code scanning. To dismiss every finding on one construct instead, use ignorePaths. Suppression docs →

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