How do you implement a "Logout" link using ASP.NET MVC? - asp.net-mvc

This seems like a pretty stupid question, but I'm trying to figure out the best way to do this. Would you simply redirect to a /Logout page and have the controller call the FormsAuthentication.SignOut function?
That was my first thought, but then I wondered if it could be abused by third party websites. Let's say someone just decides to post a link to your /Logout page. The user would get signed out of your application. Is there a good way to prevent that?

If you are concerned about a user getting accidentally logged out of you application through the use of a malicious link, you can check the Referrer to make sure that the logout is coming from your site (or is NULL in the case where the user simply types the URL in).
I actually don't worry about this since logging someone out is annoying but not necessarily a security risk.

Such a malicious link would be an example of a class of security vulnerabilities known as cross site request forgery, CSRF. A logout link is relatively harmless, but a remote site could set up a number of hidden forms and post them to your site to perform any action possible through POST.
The most common counter-measure is to include a challenge, a random hidden value in each form, and then check for that value. Checking the referer header could work, but note that some browsers don't send referer at all.
Read more: http://en.wikipedia.org/wiki/Cross-site_request_forgery

This is an old question, but here is a modern example with MVC:
[Authorize]
public RedirectResult Logout()
{
FormsAuthentication.SignOut();
return this.Redirect("/");
}
You can ensure that the Logout action is only able to be called by somebody who is logged in by applying the Authorize attribute to it.

This is what I use.
public ActionResult Logout()
{
FormsAuthentication.SignOut();
return RedirectToAction("Index", "Home");
}
Seems to work fine.
Third party websites are only going to log themselves out. So they wouldn't be achieving anything different from actually clicking Logout.

The new ASP.net MVC Beta contains an AccountController, which may be worth looking at, as it essentially implements everything from Registration to Login/Logout to Forgot Password functionality. Not sure how good it is, but a good starting Point for sure.

Derive from ActionResult
public class LogoutResult : ActionResult
{
private readonly IAuthenticationService _authenticationService;
private readonly IWebContext _context;
public LogoutResult(IAuthenticationService authenticationService, IWebContext context)
{
_authenticationService = authenticationService;
_context = context;
}
public override void ExecuteResult(ControllerContext context)
{
_authenticationService.Logout();
_context.Abandon();
_context.Redirect("~/");
}
}

You should look for a cookie or something that identifies the client as the true user.

Related

OverrideAuthentication attribute not working? ASP.NET MVC 5

I have a super simple Authentication Attribute that I'm trying to implement in an ASP.NET MVC 5 application and I'm having some trouble. I want the attribute to be applied globally, except for specific actions within a controller (for example the login form and the home page).
I've tried decorating the action with the [OverrideAuthentication] attribute with no luck. It gives me a redirect loop error because the application is still running the authentication on the login form, and keeps trying to redirect back to the login form over and over.
Has anyone else seen this behaviour? Any idea what I've stuffed up here?
By way of example, I've created a super simple filter that is currently unimplemented:
public class BasicAuthenticationAttribute
: ActionFilterAttribute, IAuthenticationFilter
{
public void OnAuthentication(AuthenticationContext filterContext)
{
throw new NotImplementedException();
}
public void OnAuthenticationChallenge(AuthenticationChallengeContext filterContext)
{
throw new NotImplementedException();
}
}
If I decorate my controller/action like this:
[BasicAuthentication]
public class AccountController : Controller
{
[HttpGet]
[OverrideAuthentication]
public ActionResult Login()
{
return View();
}
}
I get a not implemented exception when I navigate to the Login action, even though that action shouldn't be running the authentication code at all. Have I misunderstood how overrides are supposed to work?
I think you have confused authentication with authorization (as many people do). It doesn't make sense to make a [BasicAuthenticationAttribute] and register it globally, because authentication only happens upon login, not on every request.
Authorization is what takes place after the user has logged in to check whether the user has the required privileges to do a specific action, and it makes sense to do authorization globally. Authorization in MVC is handled by the [AuthorizeAttribute] and you can inherit it if you need to customize the way the authorization check is done. You can also register it as a global filter.
The [AllowAnonymousAttribute] works in conjunction with [AuthorizeAttribute], and basically tells it to skip the authorization check. It should also be noted that the [AllowAnonymousAttribute] will have no effect unless it is used with the [AuthorizeAttribute].

Prevent Url Tampering to access another users data

I just wanted to gauge opinions on how I should approach this problem and ultimately looking for a quick win (wrong way to think about things nut time pressures mean I have to think and act quickly!
I've been given a website that has a bit of an issue.
I login using standard forms authentication as User1234 and my url is as follows:
www.mywebsite.co.uk/1234/Contact.
This will take me to User1234's details.
You can put two and two together and correctly assume that 1234 is a user id of some sort.
Once authenticated, I can access the views with [Authorize] attribute present, any anonymous/unathenticated users get redirected.
However, once logged in as User1234, I can then tinker with the url like so:
www.mywebsite.co.uk/1235/Contact.
So I am authenticated as User1234 but can see User1235's data. This is BAD for obvious reasons.
When I log in, I actively set the login ID in session so in theory, I could do a check whenever a user hits an ActionResult, I could cross check the ID present in the URL against the session login ID. However, it is a rather project with lots of action results and as such, I'm reluctant to spend my Saturday afternoon adding something to each and every ActionResult.
Is there an event in the global.asax I could use that is hit on each ActionResult request where I can compare Session login ID with url ID?
Alternatively, can anyone offer some suggestions about how I can achieve this or restrict URL tampering?
You can try and do a base controller
public class BaseController : Controller
{
protected override void OnActionExecuted(ActionExecutedContext filterContext)
{
//Do your stuff here
base.OnActionExecuted(filterContext);
}
}
I assume that you don't want to change your URL routes, as you could retrieve the user id also from the session. A quick solution would be to use an ActionFilter which you can place on the affected controllers or action methods:
public class VerifyUserIdAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
var sessionUserId = filterContext.HttpContext.Session["UserId"];
var routeUserId = filterContext.RouteData.Values["UserId"];
if (routeUserId != null && sessionUserId == routeUserId)
filterContext.Result = new RedirectResult("<<url to redirect to>>");
}
}
I don't understand why the URL contains a data entry point. This appears to be a design flaw. I would remove all code that uses a URL parameter and instead make sure the controller looks up what the ID is based on the logged in user.

What is Webform's "UrlAuthorizationModule.CheckUrlAccessForPrincipal" equivalent for MVC?

I got a problem as i am writing a custom SSO solution for my company. To mkae it simple, i've made a custom authentication httpmodule that intercepts all requests so as to check user authentication state. If not authenticated, user is redirected to my custom sso login page.
The thing is, when user is not authenticated, i'd like to check if he can access the requested page/resource... With Webforms, no problem, i add an authorization block in web.config, and i use UrlAuthorizationModule.CheckUrlAccessForPrincipal with an anonymous user. Everything works fine...
But when i apply my module to an MVC (3) web site, this does not work anymore (for obvious reasons, like the possibility to access the same controller and/or action from differents urls when using routing, and because authorizations are made through controller attributes).
How can I achieve this ?? I've been searching all day long, didn't find anything about that :/
ASP.NET MVC 3 Internet Application template includes a basic AccountController which implements the following actions (along with the associated models and views):
LogOn
Register
ChangePassword / ChangePasswordSuccess
You simply need the [Authorize] attribute on the Actions or classes you wish to secure. But if you need something really custom you can do something like I've done.
I created a custom class to override security in my application.
public class AuthorizeActivityAttribute : AuthorizeAttribute
{
protected override bool AuthorizeCore(HttpContextBase httpContext)
{
HttpContext currentContext = HttpContext.Current;
//Do your custom authentication stuff here and return true or false depending on results
Return true;
}
}
And now in my Controller I have the following:
[AuthorizeActivity]
public ActionResult Index()
{
ViewBag.Message = "Welcome";
return View();
}
I had the same problem.
See solution here: MVC equivalent of Webforms "UrlAuthorizationModule.CheckUrlAccessForPrincipal"
You would have to read the information from the other controller. This
can be done by instantiating its context and the Descriptor, then
instantiating the AuthorizationContext for that controller and read
the filter info.

Designing MVC Crud with Modal problem (Not allow direct acess to Create action)

I´m have a Car View with a list of car... So, I have a Create button that opens a Modal (UI JQuery Dialog) with Site/Car/Create content...
All works fine... But I´d like to block direct access to : Site/Car/Create...
Is that possible? How?
Thanks
It's not really possible to block it completely, but you can do some things to make it more difficult. First, require that it come from a POST request. That will prevent someone from simply entering the URL with request parameters. Second, use the antiforgery token helper. That will help prevent a third-party from doing a POST to the url since they will also require both the token input and the token cookie. Third, you could potentially check if the request has the X-HTTP-REQUESTED-WITH header and only do the POST (or GET) via AJAX. It's not that hard to get around but it would prevent an accidental access if you do use GET. Fourth, and it probably should have been first, make sure that only authorized users have access to the action using the AuthorizeAttribute. Fifth, use SSL to prevent unauthorized access using FireSheep and protect your cookies and data from snooping.
In short, you won't be able to prevent a determined person with legitimate authorization from crafting a request to the action if they a really want to without using your interface. They can always craft a request that will look exactly like the one you would send. You can make it more difficult and prevent accidental access, though, using the above methods.
[AttributeUsage(AttributeTargets.Method)]
public class AjaxOnlyAttribute : ActionFilterAttribute
{
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
if (!filterContext.HttpContext.Request.IsAjaxRequest())
{
filterContext.HttpContext.Response.StatusCode = 404;
filterContext.Result = new HttpNotFoundResult();
}
else
{
base.OnActionExecuting(filterContext);
}
}
}
And then stick on your Create action like this:
[AjaxOnly]
public ActionResult Create()
{
...etc
}

Binding action parameters to request cookies in ASP.NET MVC - what happened?

In several early previews of ASP.NET MVC, arguments to controller methods would be resolved by inspecting the query string, then the form, then the cookies and server variables collections, as documented in this post from Stephen Walther.
For example, this code used to work:
public class MyController : Controller {
// This should bind to Request.Cookies["userId"].Value
public ActionResult Welcome(int userId) {
WebUser wu = WebUser.Load(userId);
ViewData["greeting"] = "Welcome, " + wu.Name;
return(View());
}
}
but now running against the release candidate, it throws an exception because it can't find a value for userId, even though userId definitely appears in the request cookies.
Was this change covered anywhere in the release notes? If this is a change to the framework, is there now a recommended alternative to binding cookies and server variables in this way?
EDIT: Thanks to those of you who have responded so far. I may have picked a bad example to demonstrate this; our code uses cookies for various forms of "convenient" but non-essential persistence (remembering ordering of search results, that kind of thing), so it's by no means purely an authentication issue. The security implications of relying on user cookies are well documented; I'm more interested in current recommendations for flexible, easily testable techniques for retrieving cookie values. (As I'm sure you can appreciate, the above example may have security implications, but is very, very easy to test!)
I believe it was the security implications that persuaded them to take these out:
The comments in Stephen Walther's post ASP.NET MVC Tip 15, leading to Phil Haack's posting User Input in Sheep's Clothing, especially his comment here:
#Troy - Step one is to dissuade devs from that line of thinking in the first place. ;) Step one prime (in parallel) is for us to remove the possibility of this line of thinking in this case.
The larger point still stands, we can make this change (after discussing it, we probably will), but that doesn't mean that it's suddenly safe to trust action method parameters.
Coupled with the complications of how you would call these methods from the various action builder classes.
I can't seem to find any explicit documentation one way or another about the controllers behaving like this other than Stephen's post, so I guess it was "quietly dropped".
I don't believe the cookies are checked anymore, and I'm not sure if it is intentional or not.
In an app against the RC I wrote recently I used the CookieContainer code from this post and a custom authorize attribute on classes like this:
public class LoginRequiredAttribute : AuthorizeAttribute
{
protected override bool AuthorizeCore(HttpContextBase httpContext)
{
IAppCookies a = new AppCookies(new CookieContainer());
return a.UserId != null; /* Better checks here */
}
}
My AppCookies.cs just has a method for UserId like this (auto resolves to int/null for you):
public int? UserId
{
get { return _cookieContainer.GetValue<int?>("UserId"); }
set { _cookieContainer.SetValue("UserId", value, DateTime.Now.AddDays(10)); }
}
Then just make sure your web.config is setup to point to your login page like this:
<authentication mode="Forms">
<forms loginUrl="~/Login"/>
</authentication>
This means in my controller to get a UserId I need to do something like this to retrieve my cookie:
[LoginRequiredAttribute]
public class RandomController : Controller
{
BaseDataContext dbContext = new BaseDataContext();
private readonly IAppCookies _cookies = new AppCookies(new CookieContainer());
public ActionResult Index()
{
return View(new RandomViewData(dbContext, _cookies.UserId));
}
}
Besides the obvious security implications, why would you need to pass the cookie through in the route anyway?
Surely you would be better off having an Authorize attribute on the action, indicating that the user should be authenticated before the action is executed.
At the end of the day, I think (hope) Microsoft has closed this as it's quite a large security issue. If this is the case, you should consider rewriting your application to comply with this.

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