What kind of Web application vulnerability likely exists in their software?

A company’s Web development team has become aware of a certain type of security vulnerability in their Web software. To mitigate the possibility of this vulnerability being exploited, the team wants to modify the software requirements to disallow users from entering HTML as input into their Web application.

What kind of Web application vulnerability likely exists in their software?
A . Cross-site scripting vulnerability
B . SQL injection vulnerability
C . Web site defacement vulnerability
D . Gross-site Request Forgery vulnerability

Answer: A