HTML scripting vulnerabilities are prevalent , but not limited to Web applications. These vulnerabilities also occur in client applications that render HTML content or write out non-HTML content that could be sniffed and interpreted as HTML. HTML scripting attacks enable an attacker to run script in a security context where the attacker is not normally allowed to author script. Many clever test cases attempt to run script when an application attempts to block or filter attacker-supplied input. You can use both the black box and white box approaches discussed in this chapter to help identify HTML scripting bugs .