HTML data-* security

[xWhiplash]

I have a question about the security of the data-* attributes in HTML.  Lets say we have some AJAX function that uses a product ID of an item.  I am trying to keep my javascript separate from my HTML.  So I would do something like this:

<a href="Product.aspx?id=7" class="select_product" data-productid="7">Product Name</a>

With jQuery, I would then do this:

$("a.select_product").click(function(e){
     e.preventDefault();

     var id = $(this).data("productid");

     //validate if ID is an integer
     if(isInt(id)){
          //call AJAX function
     }
});

So I validate the user input, but how can I validate that the specific product has that valid ID?  What is preventing somebody from using one of the many developer tools and changing data-productid to 8 or some other integer?

[lnmnky]

Nothing is stopping them. What you could do is set the function onload and have the variable set "in memory" on the object. so that the click doesn't re-run and check the variable attribute again.

 

run this on ready.....

$("a.select_product").each(function(){
 
var id = $(this).data("productid");
 
$(this).click(function(e){     
e.preventDefault();
     
     //validate if ID is an 
integer     
if(isInt(id)){          //call 
AJAX function     }});
 
});

Would this work...?

[+theblazingangel MVC]

Nothing is preventing a user from modifying things. This is why you must always validate things as necessary server-side. Any and all client-side validation should be considered to be just a nice enhancement - it can take some of the strain off the server by catching some of the most common invalid inputs in form fields, such as mandatory forms fields being left blank, and it can also potentially enhance the usability of the page, the most obvious aspect being through cutting out unnecessary page reloading.

 

Regarding your example, where a user is clicking on a product, perhaps to purchase it, and you may be worried that they could change the ID of the product they purchase; you need to implement security checks in the server-side code to prevent them doing something they shouldn't be allowed to do. If they're only allowed to purchase products with certain ID's, check the supplied ID is on that list of allowed IDs for that user. Do not submit the price of the item they are purchasing to the server via AJAX, get it from your database, and get it based on the supplied ID of the item being purchase, don't make any assumptions if there are any to be made.

 

Be mindful to not try and take things unnecessarily too far though; if a user does have the ability to change the ID of the product they are purchasing, as long as they are allowed to purchase that item, and you retrieve the correct price for it, etc, it doesn't matter. You don't need to waste time trying to block the odd rare person from doing so.

 

With that said, you should perhaps consider implementing CSRF protection, which could significantly help bolster the security for things like this.

[+theblazingangel MVC]

  On 21/06/2014 at 15:34, lunamonkey said:

Nothing is stopping them. What you could do is set the function onload and have the variable set "in memory" on the object. so that the click doesn't re-run and check the variable attribute again.

 

run this on ready.....

$("a.select_product").each(function(){
 
var id = $(this).data("productid");
 
$(this).click(function(e){     
e.preventDefault();
     
     //validate if ID is an 
integer     
if(isInt(id)){          //call 
AJAX function     }});
 
});

Would this work...?

 

Work to stop me from modifying the javascript/jQuery in the page and getting a different ID sent to the server via AJAX? No! I could always save an offline copy of the webpage to my computer, modify the code, open it in my browser and submit the form / AJAX request / whatever.

[Seahorsepip Veteran]

There's no way to prevent someone from changing values clientside, you could set the id in a database server side before you sent the page and after the user clicks the href you can check that value with the server side value.

[xWhiplash]

  On 21/06/2014 at 15:35, theblazingangel said:

Nothing is preventing a user from modifying things. This is why you must always validate things as necessary server-side. Any and all client-side validation should be considered to be just a nice enhancement - it can take some of the strain off the server by catching some of the most common invalid inputs in form fields, such as mandatory forms fields being left blank, and it can also potentially enhance the usability of the page, the most obvious aspect being through cutting out unnecessary page reloading.

 

Regarding your example, where a user is clicking on a product, perhaps to purchase it, and you may be worried that they could change the ID of the product they purchase; you need to implement security checks in the server-side code to prevent them doing something they shouldn't be allowed to do. If they're only allowed to purchase products with certain ID's, check the supplied ID is on that list of allowed IDs for that user. Do not submit the price of the item they are purchasing to the server via AJAX, get it from your database, and get it based on the supplied ID of the item being purchase, don't make any assumptions if there are any to be made.

 

Be mindful to not try and take things unnecessarily too far though; if a user does have the ability to change the ID of the product they are purchasing, as long as they are allowed to purchase that item, and you retrieve the correct price for it, etc, it doesn't matter. You don't need to waste time trying to block the odd rare person from doing so.

 

With that said, you should perhaps consider implementing CSRF protection, which could significantly help bolster the security for things like this.

 

Yeah of course the AJAX function will just retrieve the price and other stats from the database.  The only thing it will send is the ID of the product, everything else will be retrieved from the server side (if it is in stock, price, ...).  I guess it really doesn't matter.  They can use developer tools to modify the href attribute too.

 

Thanks!

[Lingwo]

You could encrypt the ID and then decrypt it server side with the ajax call and then check against it.

Would seem a tad overkill in this instance though.