How do I prevent XSS (cross-site scripting) using just HTML and PHP?
I've seen numerous other posts on this topic but I have not found an article that clear and concisely states how to actually prevent XSS.
9 Answers
Basically you need to use the function htmlspecialchars() whenever you want to output something to the browser that came from the user input.
The correct way to use this function is something like this:
echo htmlspecialchars($string, ENT_QUOTES, 'UTF-8');
Google Code University also has these very educational videos on Web Security:
One of the most important steps is to sanitize any user input before it is processed and/or rendered back to the browser. PHP has some "filter" functions that can be used.
The form that XSS attacks usually have is to insert a link to some off-site javascript that contains malicious intent for the user. Read more about it here.
You'll also want to test your site - I can recommend the Firefox add-on [XSS Me]. Looks like Easy XSS is now the way to go.
The best way to protect your input it's use htmlentities function.
Example:
htmlentities($target, ENT_QUOTES, 'UTF-8');
You can get more information here.
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