IIS7.5 ASP.NET MVC users hitting strange URLs: /(F(1xe9eXIxPz

Question

We are getting reports from a small number of users that they are ending up on very strange paths in our web app, of the form:

https://www.example.com/(F(1xe9eXIxPzMALrZu6xd_6LBxDDlJI3lH2lkSvREZZKCfPBH20SF5EcNql6uXvyBVLgiNZshp9vXxaEzuLa5zm8c4ruux6gqu3B90eXGNmKDypu-wKR4OW_GwQctfjCdoxFYcDlLwglfE6rICL3JGkxtq4jgxggiQgJopKZGzLJ_PF2lHY7NqXya8eDshkP9o8QFDad47U54TMsxEwKCki2xPV9d9VxxjmDhNg7aQb38X_OTxHtf9I7AxiccanJf4m0bo0ceEJ70Mv20XYaMSlA2))/some/path

(Note: i've changed random chars in that in case its some kind of security leak, so don't bother trying to decode it - although if doing so might be helpful, please tell me what i'm looking for so I can do it on the real URL).

This causes a 400 in IIS, but IIS doesn't log it, so I have no idea of the referrer etc.

From what our users describe, its being caused at this step:

return Redirect("/some/path");

(which is in an ASP.NET MVC 2 Controller Action).

The site running on IIS 7.5 under SSL.

Any ideas? I've never seen anything like this :s

Update:

I also have ISAPI rewrite installed, with the following .htaccess:

RewriteEngine on
AllowOverride All

# Ensure that all traffic on the live domain is enforced as HTTPS
RewriteCond %{HTTP:Host} (.*)
RewriteCond %{HTTPS} off
RewriteCond %{REQUEST_URI} (.*)
RewriteRule .? https://%1%2 [R,L]

Answer 1

We had exactly the same issue when browsing our site from iPads or Surface tablets. Forms authentication would switch to "UseUri" mode somehow.

As per http://msdn.microsoft.com/en-us/library/1d3t3c61(v=vs.90).aspx the default mode to store the Auth ticket in Forms Authentication is "UseDeviceProfile" which apparently checks whether the device supports cookies or not.

Then it goes and says "For devices that support cookies, no attempt is made to probe to determine whether cookie support is enabled.". Perhaps someone can help me understanding this sentence :)

In any case, we solved the issue by forcing Forms Authentication to use cookies in the web.config file:

<authentication mode="Forms">
  <forms cookieless="UseCookies" loginUrl="~/Login" timeout="2880" />
</authentication>

Answer 2

Take a look at Understand How the ASP.NET Cookieless Feature Works:

In V2.0, Anonymous Identification and Forms Authentication also use this feature. The URL may now look like this: http://MySite.com/MyWebApplication/(A(XXXX)S(XXXX)F(XXXX))/home.aspx

and further down:

F(XXXX): This is the Forms Authentication ticket.

Probably some of your clients block cookies.

EDIT: That said, that URL you've posted seems excessively long. Maybe the MVC internals or the URL rewriting interact with it badly for whatever reason.

Question MVC2 Cookieless Session Issue using POST might be somewhat related.

EDIT2: This thread seems to also be related to your problem: http://forums.asp.net/t/1612673.aspx. The author mentions that

some users are reporting http 400 errors

because apparently

some users are getting forms auth tokens that are longer than normal, since these are passed in the URL they are making the URL length longer than IIS will accept

Might be a long shot, but worth a try.