Overreliance on Javascript: Pen-tester's pet

I am sure all of you have been acquainted with the input validation situation where the developer validates all his input on the client-side using some poorly written Javascript to boot. Well, I recently experienced a new high in Javascript overreliance, and this was precious!!

I came across an application which relied heavily on Role Based Access Control. The Application is an Enterprise Application which has several types of users and several different "screens" that each user can access, thereby restricting the user's access based on the user's role. Well, this is how a traditional access control system works.

So, what would one do to ordinarily circumvent these controls? The first thing I tried was the URL route, where I scanned the app for URLs and entered these URLs to elevate my privileges. I was easily able to do this and the pages that clearly weren't meant for my user role kept appearing. When I tried to input some data and submit the form, the server threw me a big fat Javascript alert, "Access Denied".

Then I revoked the temporary permissions on my NoScript and the entire application fell apart. The Application so heavily relied on Javascript that the access to the links was controlled using Javascript only.

The code went something like this:

function Menu()
 {
 var UserRole=document.getElementById('userRole').value;

 switch(UserRole)
 {
 case 'elevatedPrivUser':      
  document.getElementById('thisScreen').style.display='none'; 
  break;
 case  'lowerPrivUser':       
  document.getElementById('someOtherScreen').style.display='none';
  break;
 case 'evenLowerPrivUser':
  document.getElementById('yetAnotherScreen').style.display='none';
  break;

As you can see here the Developer had left this brilliant bit of Javascript on each and every page. This was the basis of the Role Based Access Control System of the Application. Then I thought, surely, even if I accessed any one of these pages and tried to submit a request, the server would stonewall me and throw me out. I tried it out. Guess what?....More Javascript. Luckily, the Javascript wasnt available on plain view in that page, but clearly Javascript was the only validation which had been provided to validate user role and by disabling Javascript, I was able to pass my request over to the server which was accepted instantaneously.

So, the next time I go try to test an app for elevation of privileges, I will not bother with the session hijacking or the sniffing. I will just ask my NoScript to do the job and I will check whether the developer believes that "Client-side Scripting is the best!!!!"