Integrity of Hidden Fields: Asp.NET mvc

Question

We have been using asp.net mvc for development. Sometimes, we need to put some hidden fields on form that are shoved in the model by modelbinder (as expected). Nowadays, users can easily temper the form using firebug or other utilities. The purpose of hidden field is mostly to provide some information back to server on as is basis and they are not meant to be changed.

For example in my edit employee form I can put EmployeeID in hidden field but if user changes the employeeID in hidden field, wrong employee will be updated in the database. in this scenario how can we keep the integrity of hidden fields.

Answer 1

You need to enforce security to ensure that the person doing the modification has permission to do so. I'd also put the id in the URL typically rather than a hidden field, relying on the security to ensure that people don't modify things that they shouldn't be able to. If they do have permission to modify the item when changing the id manually, it shouldn't be a problem. The important thing is to make sure that a person can't change the id manually and get access to something they shouldn't. Enforcing server side permissions solves this problem. You can easily do this using Roles in conjunction with the AuthorizeAttribute.

Answer 2

if user changes the employeeID in hidden field, wrong employee will be updated in the database

This is a major security hole in your website. In everything you do with web development, no matter how clever someone's code might be or how much you think you'll be ok as long as users don't do something, remember one golden rule: Never implicitly trust data received from the client.

In order to modify anything in your website, the user must be logged in. (Right?) So in any attempt a user makes to post a form to the website (especially one which can modify data), double-check that the user submitting the form has permission perform the action being requested on the data being specified.

Ideally, every action which isn't completely public and unsecured should have a server-side permissions check. Never, ever trust what the client sends you.