AWS Cloud Development Kit と cdk-nag でアプリケーションのセキュリティとコンプライアンスを管理する

1. 以下のコマンドを実行し、AWS CDK アプリケーションを作成します。

mkdir CdkTest
cd CdkTest
cdk init app --language typescript

2. lib/cdk_test-stack.ts を、以下の内容に置き換えます。

import { Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import { Bucket } from 'aws-cdk-lib/aws-s3';

export class CdkTestStack extends Stack {
  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);
    const bucket = new Bucket(this, 'Bucket')
  }
}

3. 以下のコマンドを実行して、依存関係のインストール、および、サンプルアプリケーションの合成を行います。

npm install
npx cdk synth

1. 以下のコマンドを実行し、AWS CDK アプリケーションを作成します。

npm install cdk-nag

2. bin/cdk_test.ts を、以下の内容に置き換えます。

#!/usr/bin/env node
import 'source-map-support/register';
import * as cdk from 'aws-cdk-lib';
import { CdkTestStack } from '../lib/cdk_test-stack';
import { AwsSolutionsChecks } from 'cdk-nag'
import { Aspects } from 'aws-cdk-lib';

const app = new cdk.App();
// Add the cdk-nag AwsSolutions Pack with extra verbose logging enabled.
Aspects.of(app).add(new AwsSolutionsChecks({ verbose: true }))
new CdkTestStack(app, 'CdkTestStack', {});

3. 以下のコマンドを実行して出力結果を表示し、コンプライアンスレポートを作成します。

npx cdk synth

出力結果は、以下のようになるはずです（注：SSEはServer-side encryptionの略です）。

[Error at /CdkTestStack/Bucket/Resource] AwsSolutions-S1: The S3 Bucket has server access logs disabled. The bucket should have server access logging enabled to provide detailed records for the requests that are made to the bucket.

[Error at /CdkTestStack/Bucket/Resource] AwsSolutions-S2: The S3 Bucket does not have public access restricted and blocked. The bucket should have public access restricted and blocked to prevent unauthorized access.

[Error at /CdkTestStack/Bucket/Resource] AwsSolutions-S3: The S3 Bucket does not default encryption enabled. The bucket should minimally have SSE enabled to help protect data-at-rest.

[Error at /CdkTestStack/Bucket/Resource] AwsSolutions-S10: The S3 Bucket does not require requests to use SSL. You can use HTTPS (TLS) to help prevent potential attackers from eavesdropping on or manipulating network traffic using person-in-the-middle or similar attacks. You should allow only encrypted connections over HTTPS (TLS) using the aws:SecureTransport condition on Amazon S3 bucket policies.

Found errors

AwsSolutions NagPack をアプリケーションに適用すると、コンソールに複数のエラー（AwsSolutions-S1 、 AwsSolutions-S2 、 AwsSolutions-S3 、 AwsSolutions-S10）が表示されます。さらに、cdk.out/AwsSolutions-CdkTestStack-NagReport.csv にも、同様にエラー内容が出力されます。

Rule ID,Resource ID,Compliance,Exception Reason,Rule Level,Rule Info
"AwsSolutions-S1","CdkTestStack/Bucket/Resource","Non-Compliant","N/A","Error","The S3 Bucket has server access logs disabled."
"AwsSolutions-S2","CdkTestStack/Bucket/Resource","Non-Compliant","N/A","Error","The S3 Bucket does not have public access restricted and blocked."
"AwsSolutions-S3","CdkTestStack/Bucket/Resource","Non-Compliant","N/A","Error","The S3 Bucket does not default encryption enabled."
"AwsSolutions-S5","CdkTestStack/Bucket/Resource","Compliant","N/A","Error","The S3 static website bucket either has an open world bucket policy or does not use a CloudFront Origin Access Identity (OAI) in the bucket policy for limited getObject and/or putObject permissions."
"AwsSolutions-S10","CdkTestStack/Bucket/Resource","Non-Compliant","N/A","Error","The S3 Bucket does not require requests to use SSL."

1. lib/cdk_test-stack.ts を、以下の内容に置き換えます。

import { Stack, StackProps } from 'aws-cdk-lib';
import { Construct } from 'constructs';
import { Bucket } from 'aws-cdk-lib/aws-s3';
import { NagSuppressions } from 'cdk-nag'

export class CdkTestStack extends Stack {
  constructor(scope: Construct, id: string, props?: StackProps) {
    super(scope, id, props);
    // The local scope 'this' is the Stack. 
    NagSuppressions.addStackSuppressions(this, [
      {
        id: 'AwsSolutions-S1',
        reason: 'Demonstrate a stack level suppression.'
      },
    ])
    // Remediating AwsSolutions-S10 by enforcing SSL on the bucket.
    const bucket = new Bucket(this, 'Bucket', { enforceSSL: true })
    NagSuppressions.addResourceSuppressions(bucket, [
      {
        id: 'AwsSolutions-S2',
        reason: 'Demonstrate a resource level suppression.'
      },
    ])
  }
}

2. cdk synth コマンドを再度実行します。

npx cdk synth

以下のように出力されるはずです。

[Error at /CdkTestStack/Bucket/Resource] AwsSolutions-S3: The S3 Bucket does not default encryption enabled. The bucket should minimally have SSE enabled to help protect data-at-rest.

Found errors

cdk.out/AwsSolutions-CdkTestStack-NagReport.csv には、ルールの準拠、非準拠、抑制の詳細が記載されています。

Rule ID,Resource ID,Compliance,Exception Reason,Rule Level,Rule Info
"AwsSolutions-S1","CdkTestStack/Bucket/Resource","Suppressed","Demonstrate a stack level suppression.","Error","The S3 Bucket has server access logs disabled."
"AwsSolutions-S2","CdkTestStack/Bucket/Resource","Suppressed","Demonstrate a resource level suppression.","Error","The S3 Bucket does not have public access restricted and blocked."
"AwsSolutions-S3","CdkTestStack/Bucket/Resource","Non-Compliant","N/A","Error","The S3 Bucket does not default encryption enabled."
"AwsSolutions-S5","CdkTestStack/Bucket/Resource","Compliant","N/A","Error","The S3 static website bucket either has an open world bucket policy or does not use a CloudFront Origin Access Identity (OAI) in the bucket policy for limited getObject and/or putObject permissions."
"AwsSolutions-S10","CdkTestStack/Bucket/Resource","Compliant","N/A","Error","The S3 Bucket does not require requests to use SSL."

さらに、結果として出力された cdk.out/CdkTestStack.template.json には、cdk-nag の抑制データが含まれていることに注目してください。抑制データがリソースに含まれるため、アプリケーションに適用されなかったルールの透明性が確保されます。

{
  "Metadata": {
    "cdk_nag": {
      "rules_to_suppress": [
        {
          "id": "AwsSolutions-S1",
          "reason": "Demonstrate a stack level suppression."
        }
      ]
    }
  },
  "Resources": {
    "BucketDEB6E181": {
      "Type": "AWS::S3::Bucket",
      "UpdateReplacePolicy": "Retain",
      "DeletionPolicy": "Retain",
      "Metadata": {
        "aws:cdk:path": "CdkTestStack/Bucket/Resource",
        "cdk_nag": {
          "rules_to_suppress": [
            {
              "id": "AwsSolutions-S2",
              "reason": "Demonstrate a resource level suppression."
            }
          ]
        }
      }
    },
  ...
  },
  ...
}

import { Annotations, Match } from 'aws-cdk-lib/assertions';
import { App, Aspects, Stack } from 'aws-cdk-lib';
import { AwsSolutionsChecks } from 'cdk-nag';
import { CdkTestStack } from '../lib/cdk_test-stack';

describe('cdk-nag AwsSolutions Pack', () => {
  let stack: Stack;
  let app: App;
  // In this case we can use beforeAll() over beforeEach() since our tests 
  // do not modify the state of the application 
  beforeAll(() => {
    // GIVEN
    app = new App();
    stack = new CdkTestStack(app, 'test');

    // WHEN
    Aspects.of(stack).add(new AwsSolutionsChecks());
  });

  // THEN
  test('No unsuppressed Warnings', () => {
    const warnings = Annotations.fromStack(stack).findWarning(
      '*',
      Match.stringLikeRegexp('AwsSolutions-.*')
    );
    expect(warnings).toHaveLength(0);
  });

  test('No unsuppressed Errors', () => {
    const errors = Annotations.fromStack(stack).findError(
      '*',
      Match.stringLikeRegexp('AwsSolutions-.*')
    );
    expect(errors).toHaveLength(0);
  });
});