Securing Modern Web Apps: Content Security Policy and CORS Best Practices

1. Defense in Depth Against XSS Attacks

Cross-Site Scripting (XSS) remains one of the top web security vulnerabilities. Content Security Policy (CSP) headers restrict which external scripts, styles, and iframe origins can execute on your domain.

2. Crafting a Strict CSP Header

Content-Security-Policy: default-src 'self'; script-src 'self' https://pagead2.googlesyndication.com; img-src 'self' https: data:;

3. Understanding Cross-Origin Resource Sharing (CORS)

CORS headers instruct web browsers which third-party domains are authorized to access resource credentials over HTTP fetch calls.