What safety measures should be implemented when granting users permission to modify HTML and CSS on your site?

Question

What safety measures should be implemented when granting users permission to modify HTML and CSS on your site?

I'm really impressed by the customization options on Tumblr. Users can edit the HTML and CSS of their profiles, which is something I'd love to incorporate into my own site. However, I'm concerned about the security implications of allowing this level of customization.

Does anyone have tips or precautions for implementing a feature like Tumblr's? And should I store the editable HTML and CSS in a database? Thank you! 😊

P.S. What are your thoughts on server-side scripting? For example, if I wanted users to be able to script a button that interacts with the database. How would I go about doing this?

html css customization security

Answer 1

Answer №1

Ensuring that users can utilize all aspects of HTML/CSS while maintaining security is quite challenging. One approach could be to remove all CSS and HTML attributes, allowing only designated "safe" code on a whitelist.

Illustrations

<p>This snippet is acceptable.</p>

<p><a onload="alert('XSS!')">Undesirable attribute should be removed.</a></p>

<p><a href="http://google.com/" class="blue">Valid hyperlink.</a>
Remember to sanitize the href attribute!</p>

<h1>Improper formatting may lead to issues,
so ensure proper closure

<style>
.blue {
    color: #00f; // retain this (via whitelist)
    strange-css-rule: potentially risky; // Exclude this!
}
</style>

These are just a few examples of common challenges.

While I'm not well-versed in Tumblr's methods, they likely employ a similar strategy.

In terms of storing HTML and CSS in a database, it is indeed feasible and many systems adopt this approach. For simplicity, maintain a singular representation to prevent user confusion ("Why isn't my CSS being applied when it's clearly in the code!")

Answer 2

Ensuring that users can utilize all aspects of HTML/CSS while maintaining security is quite challenging. One approach could be to remove all CSS and HTML attributes, allowing only designated "safe" code on a whitelist.

Illustrations

<p>This snippet is acceptable.</p>

<p><a onload="alert('XSS!')">Undesirable attribute should be removed.</a></p>

<p><a href="http://google.com/" class="blue">Valid hyperlink.</a>
Remember to sanitize the href attribute!</p>

<h1>Improper formatting may lead to issues,
so ensure proper closure

<style>
.blue {
    color: #00f; // retain this (via whitelist)
    strange-css-rule: potentially risky; // Exclude this!
}
</style>

These are just a few examples of common challenges.

While I'm not well-versed in Tumblr's methods, they likely employ a similar strategy.

In terms of storing HTML and CSS in a database, it is indeed feasible and many systems adopt this approach. For simplicity, maintain a singular representation to prevent user confusion ("Why isn't my CSS being applied when it's clearly in the code!")

Answer 3

Answer №2

In the case that you are utilizing php, a mini API system can be utilized for handling database issues. For instance, if you wish to enable users to comment on something and store it in your database, an API like the following can be used.

To begin, create an api.php file (URL Location: http://yoursite.com/api.php)

<?php

// ID and Key may vary per user.
// id = 1234
// key = 'secret_key'

// function = name of the function that can be called by the user
// option = parameter passed to the function

// Check if id, key, function, and option are requested before proceeding to call the function.

if(isset($_GET['id'], $_GET['key'], $_GET['function'], $_GET['option'])) {
   $id = $_GET['id'];
   $key = $_GET['key'];

   if($id == '1234' && $key == 'secret_key') {

       // Define all functions here
       function make_comment($option) {
           ...code for saving comment to database...
       }

       if(function_exists($_GET['function'])) {
           $_GET['function']($_GET['option']);
       }
   }
}

?>

Users can then call this function from any button with a simple API call, such as:

<a href='http://yoursite.com/api.php?id=1234&key=secret_key&function=make_comment&option=i_am_comment'></a>

Answer 4

In the case that you are utilizing php, a mini API system can be utilized for handling database issues. For instance, if you wish to enable users to comment on something and store it in your database, an API like the following can be used.

To begin, create an api.php file (URL Location: http://yoursite.com/api.php)

<?php

// ID and Key may vary per user.
// id = 1234
// key = 'secret_key'

// function = name of the function that can be called by the user
// option = parameter passed to the function

// Check if id, key, function, and option are requested before proceeding to call the function.

if(isset($_GET['id'], $_GET['key'], $_GET['function'], $_GET['option'])) {
   $id = $_GET['id'];
   $key = $_GET['key'];

   if($id == '1234' && $key == 'secret_key') {

       // Define all functions here
       function make_comment($option) {
           ...code for saving comment to database...
       }

       if(function_exists($_GET['function'])) {
           $_GET['function']($_GET['option']);
       }
   }
}

?>

Users can then call this function from any button with a simple API call, such as:

<a href='http://yoursite.com/api.php?id=1234&key=secret_key&function=make_comment&option=i_am_comment'></a>

What safety measures should be implemented when granting users permission to modify HTML and CSS on your site?

Answer №1

Illustrations

Answer №2

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