how to change session id after login in asp.net

Question

I have a website that's using forms authentication and membership. A user must have cookies enabled to use the site. I've been asked to change the code so that the session id is changed as soon as a user logs in. Aparently this will protect against a Session Fixation attack (http://en.wikipedia.org/wiki/Session_fixation). Does anyone know how I can change the session id without losing the whole session ? PHP has a specific method for doing this but I can't find a .NET equivalent.

Answer 1

Here's a blog post that talks about this:

ASP.NET does not directly support functionality to regenerate a session ID. See the documentation regarding the issue here. There is a not-so quick and dirty way to do it by setting the ASPNET_SessionID value to the empty string and redirecting so that the value is regenerated.

Answer 2

I have answered a similar question at Generating a new ASP.NET session in the current HTTPContext. Basically we must change some of the SessionStateModule internal state to be able to regenerate session ID without losing objects in the Session. I used reflection to set the _rqId field to the new ID and _rqSessionStateNotFound to true. The downside is we must grant "Full Trust" to the Application.

Answer 3

This is a really old question I'm resurrecting, but here's the solution:

var manager = new SessionIDManager();
bool redirected, isAdded;
manager.SaveSessionID(System.Web.HttpContext.Current, 
    "5vonjb4mtb1of2fxvhjvkh5d", out redirected, out isAdded);

// sessionId now equals "5vonjb4mtb1of2fxvhjvkh5d"
var sessionId = Session.SessionID;