Securing Your API Gateway with AWS WAF using CloudFormation
Protecting your APIs from threats is crucial. While AWS API Gateway provides built-in security features, it's often beneficial to add an extra layer of defense using AWS Web Application Firewall (WAF). WAF acts as a shield, filtering out malicious traffic before it reaches your backend resources. This article guides you through securely integrating WAF with your API Gateway using a CloudFormation template, ensuring a streamlined and efficient deployment process.
The Problem:
Manually configuring WAF and its rules for each API Gateway endpoint can be tedious and error-prone. CloudFormation allows us to automate this process, ensuring consistency and repeatability across deployments.
Scenario:
Imagine you have an API Gateway endpoint that handles user registration. You want to protect it from common web attacks like SQL injection and cross-site scripting (XSS).
Original Code (CloudFormation Template):
Resources:
MyApiGateway:
Type: AWS::Serverless::Api
Properties:
Name: MyApi
DefinitionBody:
openapi: 3.0.1
info:
title: My API
version: v1
paths:
/register:
post:
requestBody:
content:
application/json:
schema:
$ref: '#/components/schemas/User'
responses:
'200':
description: OK
MyWafWebAcl:
Type: AWS::WAFv2::WebACL
Properties:
Name: MyWafWebAcl
DefaultAction: ALLOW
Scope: REGIONAL
Rules:
- Name: BlockSQLInjection
Priority: 1
Action:
Block: {}
Statement:
Statement:
AndStatement:
Statements:
- Statement:
ByteMatchStatement:
FieldToMatch:
SingleHeader:
Name: "Host"
PositionalConstraint: CONTAINS
SearchString: "union"
TextTransformations:
- Type: NONE
- Statement:
ByteMatchStatement:
FieldToMatch:
SingleHeader:
Name: "Referer"
PositionalConstraint: CONTAINS
SearchString: "evil.com"
TextTransformations:
- Type: NONE
Analysis and Insights:
- WAF Integration: The template creates a WAF Web ACL (Web Access Control List) named "MyWafWebAcl". This Web ACL defines rules to block requests containing specific strings, like "union" (for SQL injection) and "evil.com" (for cross-site scripting).
- Default Action: The
DefaultActionis set toALLOW, meaning all requests pass through unless explicitly blocked by a rule. - Rule Structure: Each rule includes a
Name,Priority(determining the order of rule execution),Action(block or allow), andStatement(the logic to match requests). - Byte Match Statement: The
ByteMatchStatementmatches specific strings within the request headers (in this example, the "Host" and "Referer" headers).
Additional Value:
- Customizable Rules: You can create more complex rules based on your specific security requirements.
- Centralized Management: CloudFormation allows you to manage your WAF rules and API Gateway configuration in a single, version-controlled template.
- Rollback Capabilities: In case of deployment issues, CloudFormation facilitates easy rollbacks to previous working configurations.
Further Exploration:
- WAF Rules: AWS offers a rich set of rule types, including rate-based rules, geo-match rules, and more. Explore the AWS documentation for a complete list and guidance on crafting effective rules.
- API Gateway Integration: You can further refine the integration by associating the WAF Web ACL with specific API Gateway stages (like "dev" or "prod").
- Monitoring and Logging: Leverage CloudWatch logs to monitor WAF activity and analyze blocked requests.
References:
By implementing this secure architecture, you can confidently protect your API Gateway endpoints from malicious attacks and ensure a safe and reliable API experience.
