# Are my forms a danger towards code injection?

I'm writing a PHP tutorial and I would like to display some forms where the users could enter values that are displayed in the same webpage, just as a demonstration.

The forms do nothing special, they only use print instructions to display the input.

I would like to know if these apparently innofensive forms could be a real danger for my server because of script injection.

The code that processes the form is:

<?php
if (array_key_exists('user', $_POST)) { print "Hello, " .$_POST['user'];
} else {
}
?>

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I think it would be helpful to include the relevant code in your question. –  unor Jan 23 at 16:48
<?php if (array_key_exists('user', $_POST)) { print "Hello, " .$_POST['user']; } else { print "Waiting for your input..."; } ?> –  Sakhal Turkaystan Jan 23 at 16:51

## migrated from webmasters.stackexchange.comJan 24 at 18:29

This question came from our site for pro webmasters.

The Short answer is yes you are vulnerable to injection. XSS to be precise which you can read more about here https://www.owasp.org/index.php/XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet

Explaination:

All user input should be sanatized for example:

if you input <script>alert("This will alert");</script> into your form you will notice an alert message will appear on your page

however if you sanatize the code i.e.

print "Hello, " . htmlentities(\$_POST['user']);


you will no longer see the alert message

using htmlentities() will help protect you from the script injection.

You would also be better validating the data that will be expected from the user

Other points which you can see here http://stackoverflow.com/questions/11554432/php-post-dynamic-variable-names-security-concerns which are based more on dynamically creating variables

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Also, apart from the security aspect, if you don't convert special HTML characters (in the user input) to HTML entities when you output in the HTML page then the user might not even see what they have just entered and to the user your script might not appear to be working correctly - unless that is also part of the tutorial? –  w3d Jan 23 at 22:40
@w3d good point I will add that later. –  Liam Sorsby Jan 23 at 22:54
Yes, I understand. I have already applied htmlentities() to the input. Allowing the user to insert code is not a part of the tutorial, albeit it would be interesting that it were, but I'm too afraid to let people to put scripts in there. It would be too much risk to withstand. –  Sakhal Turkaystan Jan 24 at 8:15
@RobApodaca I've updated my answer –  Liam Sorsby Jan 26 at 20:15
Beside the fact that if the input contains < the output might not be what you expected, the real dangers you face are XSS and CSRF.