Secure Checkout

Overview

Payment pages are the highest-value target for attackers — a single XSS vulnerability can lead to Magecart-style card skimming attacks that steal thousands of card numbers. Securing checkout requires enforcing TLS everywhere, implementing strict Content Security Policies (CSP) to prevent script injection, using payment tokenization to minimize PCI scope, and removing non-essential third-party scripts from payment pages. The good news: Shopify and BigCommerce handle most of this infrastructure automatically. WooCommerce merchants need to configure hosting and install security plugins. Custom storefronts require implementing all of these controls from scratch.

When to Use This Skill

• When building or auditing a checkout flow that accepts payment information
• When a penetration test or security scan surfaces XSS, CSP, or header vulnerabilities on payment pages
• When reviewing third-party script loading on pages that have access to payment form context
• When preparing for PCI DSS SAQ A-EP or SAQ D compliance assessment
• When migrating from a hosted payment page to a custom UI (increases PCI scope)

Core Instructions

Step 1: Understand your checkout security responsibility by platform