A7 – Preventing Cross-Site Scripting

Cross-Site Scripting, as seen previously, happens when the data shown to the user is not correctly encoded and the browser interprets it as script code and executes it. This also has an input validation factor, as a malicious code is usually inserted through input variables.

In this recipe, we will cover the input validation and output encoding required for developers to prevent XSS vulnerabilities in their applications.

How to do it...

1. The first sign of an application being vulnerable to XSS is that, in the page, it reflects the exact input given by the user. So try not to use user-given information to build output text.
2. When you need to put user-provided data in the output page...