Question

I have a script that registers users based on their user input. This uses prepared statements plus whitelists to prevent sql injection. But I am struggling to understand the prevention of XSS.

From what I understand, you only need to prevent XSS if you are outputting HTML onto the page? What does this mean???

Im guessing that with this register page it doesn’t apply because I am not outputting HTML to the web page? Is that right?

If I was to prevent XSS, do I use htmlspecialchars?

Answer 1

Generally correct, if you are having any returned values show up on the page, or if you are inserting information into the database for later retrieval and display (like user profile information) you will want to use htmlspecialchars.

For me, when I do my user registration, if they fail to enter a correct value in an input field, I redisplay the page with the values they entered. In this case, I have it encoded with htmlspecialchars.

If at any point ever, you plan on redisplaying the information from the DB into a webpage (as mentioned with profiles and the like) you should use htmlspecialchars.

Better safe than sorry I always say – never trust user input