Using AWS WAF to protect your APIs

AWS WAF is a web application firewall that helps protect web applications and APIs from attacks. It enables you to configure a set of rules called a web access control list (web ACL) that allow, block, or count web requests based on customizable web security rules and conditions that you define. For more information, see How AWS WAF Works.

You can use AWS WAF to protect your API Gateway REST API from common web exploits, such as SQL injection and cross-site scripting (XSS) attacks. These could affect API availability and performance, compromise security, or consume excessive resources. For example, you can create rules to allow or block requests from specified IP address ranges, requests from CIDR blocks, requests that originate from a specific country or region, requests that contain malicious SQL code, or requests that contain malicious script.

You can also create rules that match a specified string or a regular expression pattern in HTTP headers, method, query string, URI, and the request body (limited to the first 8 KB). Additionally, you can create rules to block attacks from specific user agents, bad bots, and content scrapers. For example, you can use rate-based rules to specify the number of web requests that are allowed by each client IP in a trailing, continuously updated, 5-minute period.

Important

AWS WAF is your first line of defense against web exploits. When AWS WAF is enabled on an API, AWS WAF rules are evaluated before other access control features, such as resource policies, IAM policies, Lambda authorizers, and Amazon Cognito authorizers. For example, if AWS WAF blocks access from a CIDR block that a resource policy allows, AWS WAF takes precedence and the resource policy isn't evaluated.

To enable AWS WAF for your API, you need to do the following:

1. Use the AWS WAF console, AWS SDK, or CLI to create a web ACL that contains the desired combination of AWS WAF managed rules and your own custom rules. For more information, see Getting Started with AWS WAF and Web access control lists (web ACLs).

   Important

   API Gateway requires an AWS WAFV2 web ACL for a Regional application or an AWS WAF Classic Regional web ACL.

2. Associate the AWS WAF web ACL with an API stage. You can do this by using the AWS WAF console, AWS SDK, CLI, or by using the API Gateway console.

To associate an AWS WAF web ACL with an API Gateway API stage using the API Gateway console

To use the API Gateway console to associate an AWS WAF web ACL with an existing API Gateway API stage, use the following steps:

1. Sign in to the API Gateway console at https://console.aws.amazon.com/apigateway.

2. Choose an existing API or create a new one.

3. In the main navigation pane, choose Stages, and then choose a stage.

4. In the Stage details section, choose Edit.

5. Under Web application firewall (AWS WAF), select your web ACL.

   If you are using AWS WAFV2, select an AWS WAFV2 web ACL for a Regional application. The web ACL and any other AWS WAFV2 resources that it uses must be located in the same Region as your API.

   If you are using AWS WAF Classic Regional, select a Regional web ACL.

6. Choose Save changes.

Associate an AWS WAF web ACL with an API Gateway API stage using the AWS CLI

To use the AWS CLI to associate an AWS WAFV2 web ACL for a Regional application with an existing API Gateway API stage, call the associate-web-acl command, as in the following example:

aws wafv2 associate-web-acl \
--web-acl-arn  arn:aws:wafv2:{region}:111122223333:regional/webacl/test-cli/a1b2c3d4-5678-90ab-cdef-EXAMPLE11111 \
--resource-arn arn:aws:apigateway:{region}::/restapis/4wk1k4onj3/stages/prod

To use the AWS CLI to associate an AWS WAF Classic Regional web ACL with an existing API Gateway API stage, call the associate-web-acl command, as in the following example:

aws waf-regional associate-web-acl \
--web-acl-id 'aabc123a-fb4f-4fc6-becb-2b00831cadcf' \
--resource-arn 'arn:aws:apigateway:{region}::/restapis/4wk1k4onj3/stages/prod'

Associate an AWS WAF web ACL with an API stage using the AWS WAF REST API

To use the AWS WAFV2 REST API to associate an AWS WAFV2 web ACL for a Regional application with an existing API Gateway API stage, use the AssociateWebACL command, as in the following example:

import boto3
 
wafv2 = boto3.client('wafv2')

wafv2.associate_web_acl(
    WebACLArn='arn:aws:wafv2:{region}:111122223333:regional/webacl/test/abc6aa3b-fc33-4841-b3db-0ef3d3825b25',
    ResourceArn='arn:aws:apigateway:{region}::/restapis/4wk1k4onj3/stages/prod'
)

To use the AWS WAF REST API to associate an AWS WAF Classic Regional web ACL with an existing API Gateway API stage, use the AssociateWebACL command, as in the following example:

import boto3
 
waf = boto3.client('waf-regional')
 
waf.associate_web_acl(
    WebACLId='aabc123a-fb4f-4fc6-becb-2b00831cadcf',
    ResourceArn='arn:aws:apigateway:{region}::/restapis/4wk1k4onj3/stages/prod'
)