In a new post to his site Christoph Rumpel shares an introduction to the use of Content Security policies to prevent client-side security issues in your applications. While his examples are more Laravel-specific, the concepts can be applied to just about any framework or home-grown solution.

As more and more services get digital these days, security has become a significant aspect of every application. Especially when it comes to third-party code, it is tough to guarantee safety. But in general, XSS and Code Injection is a big problem these days. Content Security Policy provides another layer of security that helps to detect and protect different attacks. Today, I will introduce this concept and its main features, as well as show real-world examples.

He starts with a general look at web application security vulnerabilities and, more specifically, cross-site scripting issues. These are the ones that a Content Security Policy (CSP) can help prevent. He then covers the basics of the CSP header and gets into the implementation. In his example he sets up the addition of the CSP header as a middleware so that it's included on every request. With the default header all resources are blocked so he walks through the process of restoring access to the scripts, fonts and styles his blog needs to work correctly.

With the basics covered he then gets into a few more advanced features of CSP policies such as nonces for resource identification, iframe handling and the submission of forms. The post ends with a recommendation of the Laravel CSP package for use in Laravel applications. If you're looking for something more framework agnostic you might want to look into ParagonIE's CSP Builder library.