How do I protect a website against XSS attacks with AWS WAF?

In this guide, we will configure AWS WAF to protect a website from Cross-Site Scripting (XSS) attacks. AWS WAF (Web Application Firewall) is a service that helps protect web applications by filtering and monitoring HTTP requests. We will create an XSS Match Set, a WAF Rule, and a Web ACL (Access Control List) that attaches to our CloudFront distribution to block malicious requests.

import * as aws from "@pulumi/aws";

// Define an XSS Match Set to identify XSS patterns in requests
const xssMatchSet = new aws.waf.XssMatchSet("xssMatchSet", {
    name: "xssMatchSet",
    xssMatchTuples: [{
        fieldToMatch: {
            type: "QUERY_STRING", // Check the query string for XSS patterns
        },
        textTransformation: "NONE", // No transformation on the text
    }],
});

// Create a WAF Rule that uses the XSS Match Set
const wafRule = new aws.waf.Rule("wafRule", {
    name: "xssRule",
    metricName: "xssRuleMetric",
    predicates: [{
        dataId: xssMatchSet.id,
        negated: false,
        type: "XssMatch",
    }],
});

// Create a Web ACL to attach to our CloudFront distribution
const webAcl = new aws.waf.WebAcl("webAcl", {
    name: "webAcl",
    metricName: "webAclMetric",
    defaultAction: {
        type: "ALLOW",
    },
    rules: [{
        action: {
            type: "BLOCK",
        },
        priority: 1,
        ruleId: wafRule.id,
    }],
});

// Output the Web ACL ID
export const webAclId = webAcl.id;

Key Points

1. XSS Match Set: This resource defines the patterns to look for in HTTP requests to identify potential XSS attacks.
2. WAF Rule: This rule uses the XSS Match Set to block requests that match the defined patterns.
3. Web ACL: This Access Control List is attached to a CloudFront distribution to enforce the WAF rules and block malicious requests.

Summary

In this guide, we configured AWS WAF to protect a website from XSS attacks. We created an XSS Match Set to define the patterns to look for, a WAF Rule to use this match set, and a Web ACL to apply the rule to our CloudFront distribution. This setup helps to block malicious requests and protect your web application from XSS vulnerabilities.