Practical Security

Cross-Site Scripting (XSS)

We’ve seen the knock-knock joke principle applied to SQL (SQL injection). Let’s take a look at attacks using that same principle when applied to the HTML and JavaScript in a web page. We call this attack cross-site scripting (or XSS for short) if the attack injects JavaScript. We call it DOM injection if it injects regular HTML.

Let’s continue with the example from earlier in the chapter of a blogging site. One of the most basic requirements is for anyone using the site to be able to read posts written by other users. Suppose a reader writes a blog post such as this:

Dear Diary, Today I read the most wonderful book, Practical Security.

The reader would expect to be able to see this blog post in their browser. But what ...