As a result of a penetration test against some of our products in the pipeline, what looked to be at the time an 'easy' problem to fix is turning out to be a toughy.
Not that it should of course, I mean why would just generating a brand new session for the current HTTPContext be so difficult? Bizarre! Anyway- I've written a cheeky little utility class to "just do it":
(apologies for code formatting/highlighting/Visual Basic I must be doing something wrong)
Imports System.Web
Imports System.Web.SessionState
Public Class SwitchSession
Public Shared Sub SetNewSession(ByVal context As HttpContext)
' This value will hold the ID managers action to creating a response cookie
Dim cookieAdded As Boolean
' We use the current session state as a template
Dim state As HttpSessionState = context.Session
' We use the default ID manager to generate a new session id
Dim idManager As New SessionIDManager()
' We also start with a new, fresh blank state item collection
Dim items As New SessionStateItemCollection()
' Static objects are extracted from the current session context
Dim staticObjects As HttpStaticObjectsCollection = _
SessionStateUtility.GetSessionStaticObjects(context)
' We construct the replacement session for the current, some parameters are new, others are taken from previous session
Dim replacement As New HttpSessionStateContainer( _
idManager.CreateSessionID(context), _
items, _
staticObjects, _
state.Timeout, _
True, _
state.CookieMode, _
state.Mode, _
state.IsReadOnly)
' Finally we strip the current session state from the current context
SessionStateUtility.RemoveHttpSessionStateFromContext(context)
' Then we replace the assign the active session state using the replacement we just constructed
SessionStateUtility.AddHttpSessionStateToContext(context, replacement)
' Make sure we clean out the responses of any other inteferring cookies
idManager.RemoveSessionID(context)
' Save our new cookie session identifier to the response
idManager.SaveSessionID(context, replacement.SessionID, False, cookieAdded)
End Sub
End Class
It works fine for the remainder of the request, and correctly identifies itself as the new session (e.g. HTTPContext.Current.Session.SessionID returns the newly generated session identifier).
Surprise surprise then, that when the next request hits the server, the HTTPContext.Session (an HTTPSessionState object) identifies itself with the correct SessionID, but has IsNewSession set to True, and is empty, losing all the session values set in the previous request.
So there must be something special about the previous HTTPSessionState object being removed from the initial request, an event handler here, a callback there, something which handles persisting the session data across requests, or just something I'm missing?
Anybody got any magic to share?
I would like to share my magic. Actually, no, its not yet magical.. We ought to test and evolve the code more. I only tested these code in with-cookie, InProc session mode. Put these method inside your page, and call it where you need the ID to be regenerated (please set your web app to Full Trust):
void regenerateId()
{
System.Web.SessionState.SessionIDManager manager = new System.Web.SessionState.SessionIDManager();
string oldId = manager.GetSessionID(Context);
string newId = manager.CreateSessionID(Context);
bool isAdd = false, isRedir = false;
manager.SaveSessionID(Context, newId, out isRedir, out isAdd);
HttpApplication ctx = (HttpApplication)HttpContext.Current.ApplicationInstance;
HttpModuleCollection mods = ctx.Modules;
System.Web.SessionState.SessionStateModule ssm = (SessionStateModule)mods.Get("Session");
System.Reflection.FieldInfo[] fields = ssm.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance);
SessionStateStoreProviderBase store = null;
System.Reflection.FieldInfo rqIdField = null, rqLockIdField = null, rqStateNotFoundField = null;
foreach (System.Reflection.FieldInfo field in fields)
{
if (field.Name.Equals("_store")) store = (SessionStateStoreProviderBase)field.GetValue(ssm);
if (field.Name.Equals("_rqId")) rqIdField = field;
if (field.Name.Equals("_rqLockId")) rqLockIdField = field;
if (field.Name.Equals("_rqSessionStateNotFound")) rqStateNotFoundField = field;
}
object lockId = rqLockIdField.GetValue(ssm);
if ((lockId != null) && (oldId !=null)) store.ReleaseItemExclusive(Context, oldId, lockId);
rqStateNotFoundField.SetValue(ssm, true);
rqIdField.SetValue(ssm, newId);
}
I have been digging around .NET Source code (that were available in http://referencesource.microsoft.com/netframework.aspx), and discovered that there is no way I could regenerate SessionID without hacking the internals of session management mechanism. So I do just that - hack SessionStateModule internal fields, so it will save the current Session into a new ID. Maybe the current HttpSessionState object still has the previous Id, but AFAIK the SessionStateModule ignored it. It just use the internal _rqId field when it has to save the state somewhere. I have tried other means, like copying SessionStateModule into a new class with a regenerate ID functionality, (I was planning to replace SessionStateModule with this class), but failed because it currently has references to other internal classes (like InProcSessionStateStore). The downside of hacking using reflection is we need to set our application to 'Full Trust'.
Oh, and if you really need the VB version, try these :
Sub RegenerateID()
Dim manager
Dim oldId As String
Dim newId As String
Dim isRedir As Boolean
Dim isAdd As Boolean
Dim ctx As HttpApplication
Dim mods As HttpModuleCollection
Dim ssm As System.Web.SessionState.SessionStateModule
Dim fields() As System.Reflection.FieldInfo
Dim rqIdField As System.Reflection.FieldInfo
Dim rqLockIdField As System.Reflection.FieldInfo
Dim rqStateNotFoundField As System.Reflection.FieldInfo
Dim store As SessionStateStoreProviderBase
Dim field As System.Reflection.FieldInfo
Dim lockId
manager = New System.Web.SessionState.SessionIDManager
oldId = manager.GetSessionID(Context)
newId = manager.CreateSessionID(Context)
manager.SaveSessionID(Context, newId, isRedir, isAdd)
ctx = HttpContext.Current.ApplicationInstance
mods = ctx.Modules
ssm = CType(mods.Get("Session"), System.Web.SessionState.SessionStateModule)
fields = ssm.GetType.GetFields(System.Reflection.BindingFlags.NonPublic Or System.Reflection.BindingFlags.Instance)
store = Nothing : rqLockIdField = Nothing : rqIdField = Nothing : rqStateNotFoundField = Nothing
For Each field In fields
If (field.Name.Equals("_store")) Then store = CType(field.GetValue(ssm), SessionStateStoreProviderBase)
If (field.Name.Equals("_rqId")) Then rqIdField = field
If (field.Name.Equals("_rqLockId")) Then rqLockIdField = field
If (field.Name.Equals("_rqSessionStateNotFound")) Then rqStateNotFoundField = field
Next
lockId = rqLockIdField.GetValue(ssm)
If ((Not IsNothing(lockId)) And (Not IsNothing(oldId))) Then store.ReleaseItemExclusive(Context, oldId, lockId)
rqStateNotFoundField.SetValue(ssm, True)
rqIdField.SetValue(ssm, newId)
End Sub