Securing ASP.NET MVC3 Controllers/Actions - asp.net-mvc

Question

I am designing an MVC 3 application where multiple tenants reside in a single database.
What is the best way to prevent users from editing/viewing other tenants data in MVC? (i.e. someone could type in '/People/Edit/1' and edit the person with Id of 1- regardless of wether they are part of the tenants data or not).
I know I can override 'OnActionExecuting(ActionExecutingContext filterContext)' for each controller- but it sounds crazy to have to handle each action seperately, get the ID or OBJECT depending on if its a POST or GET and then check if the operation is allowed.
Any better ideas?
Also, I do not want to go down the route of creating a different database or schema for each tenant.
Thanks in advance.

Answer 1

Instead of passing ids to your controller actions write a custom model binder for your entities which will fetch it from the database. So for example let's assume that you have the following model:
public class Person
{
public string Id { get; set; }
... some other properties
}
Now instead of having:
[HttpPost]
public ActionResult Edit(string id)
{
...
}
write:
[HttpPost]
public ActionResult Edit(Person person)
{
...
}
and then write a custom model binder for Person:
public class PersonModelBinder : IModelBinder
{
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
var id = bindingContext.ValueProvider.GetValue("id");
// check if an id was provided and if the user is authenticated
if (!controllerContext.HttpContext.User.Identity.IsAuthenticated || id == null)
{
throw new HttpException(403, "Forbidden");
}
var currentUser = controllerContext.HttpContext.User.Identity.Name;
// fetch the person from your repository given the id and belonging
// to the currently authenticated user
var person = _repository.GetPerson(id.AttemptedValue, currentUser);
if (person == null)
{
// no person found matching
throw new HttpException(403, "Forbidden");
}
return person;
}
}
which you would register in Application_Start:
ModelBinders.Binders.Add(typeof(Person), new PersonModelBinder());

Answer 2

Original answer
To solve the problem quickly use guids instead of a auto-increasing integer. However this is just delaying the problem.
One of the things you can do is to role your own authorize attribuut http://msdn.microsoft.com/en-us/library/system.web.mvc.authorizeattribute.aspx Or you can chose to create a global actionfilter. http://www.asp.net/mvc/tutorials/understanding-action-filters-cs
Addition information on how you could do it based on request in comment
public class MySuperFilter : ActionFilterAttribute
{
//Called by the MVC framework before the action method executes.
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
String user = filterContext.HttpContext.User.Identity.Name;
int id = int.Parse(filterContext.RouteData.GetRequiredString("Id"));
if (!IsValidUser(user,id))
{
filterContext.Result = new RedirectToRouteResult(
new RouteValueDictionary {{ "Controller", "YourController" },
{ "Action", "YourAction" } });
}
base.OnActionExecuting(filterContext);
}
private bool IsValidUser(string user,int id)
{
//Check if the user has acces to the page
return true;
}
}

Answer 3

It's a non-elegant solution but depending on scope it could be easiest. Having designed a similar system that has relatively few points of entry for multiple tenants data we just merely check that the CurrentUser is the Owner of the object that is being queried. Our use objects a common base interface that has the owner field so the check is made not carrying about the specific object but just from the interface. If there's a mismatch we throw a security exception and log that a user is probably playing around the query string seeing if they get our website to leak data the way many production websites do.