What is cross-site scripting? Cross-site scripting, also known as XSS, is a class of security exploit that has gotten a fair bit of attention in the last few years. Many users, and even Web developers, aren't entirely clear on what the term means, however. I'll explain cross-site scripting for you, so you will know where the dangers lie. Cross-site scripting, also known as XSS, is a class of security exploit that has gotten a fair bit of attention in the last few years.