A Web Developer's Guide to Cross-Site Scripting

Cross-site scripting attacks are those in which attackers inject malicious code, usually client-side scripts, into web applications from outside sources. Because of the number of possible injection locations and techniques, many applications are vulnerable to this attack method. Scripting attacks differ from other web application vulnerabilities because they attack an application's users, not an application's infrastructure, but they can still cause a great deal of damage. This paper describes how cross-site scripting works and what makes an application vulnerable, along with suggestions for developers about tools for discovering cross-site scripting vulnerabilities in their applications and recommended practices for creating applications that are less vulnerable to the attack and more resilient against successful cross-site scripting attacks.