Generating a new ASP.NET session in the current HTTPContext

Question

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.

Answer 1

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

Answer 2

Can you not just set:

<sessionState regenerateExpiredSessionId="False" />

in web.config, and then use the solution suggested by Ahmad?

Answer 3

Have you considered using the HttpSessionState.Abandon method? That ought to clear everything. Then start a new session and populate it with all the items you stored from your code above.

Session.Abandon(); should suffice. Otherwise you could try to go the extra mile with a few more calls if it's still being stubborn:

Session.Contents.Abandon();
Session.Contents.RemoveAll(); 

Answer 4

If you're security concious and would like the C# version of this answer removing the old field, please use the following.

private static void RegenerateSessionId()
{

    // Initialise variables for regenerating the session id
    HttpContext Context = HttpContext.Current;
    SessionIDManager manager = new SessionIDManager();
    string oldId = manager.GetSessionID(Context);
    string newId = manager.CreateSessionID(Context);
    bool isAdd = false, isRedir = false;

    // Save a new session ID
    manager.SaveSessionID(Context, newId, out isRedir, out isAdd);

    // Get the fields using the below and create variables for storage
    HttpApplication ctx = HttpContext.Current.ApplicationInstance;
    HttpModuleCollection mods = ctx.Modules;
    SessionStateModule ssm = (SessionStateModule)mods.Get("Session");
    FieldInfo[] fields = ssm.GetType().GetFields(BindingFlags.NonPublic | BindingFlags.Instance);
    SessionStateStoreProviderBase store = null;
    FieldInfo rqIdField = null, rqLockIdField = null, rqStateNotFoundField = null;
    SessionStateStoreData rqItem = null;

    // Assign to each variable the appropriate field values
    foreach (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;
        if (field.Name.Equals("_rqItem")) rqItem = (SessionStateStoreData)field.GetValue(ssm);
    }

    // Remove the previous session value
    object lockId = rqLockIdField.GetValue(ssm);
    if ((lockId != null) && (oldId != null))
        store.RemoveItem(Context, oldId, lockId, rqItem);

    rqStateNotFoundField.SetValue(ssm, true);
    rqIdField.SetValue(ssm, newId);
}

Answer 5

As Can Gencer mentioned - ReleaseItemExclusive doesn't remove old session from the store and that leads to that session eventually expiring and calling Session_End in Global.asax. This caused us a huge problem in production, because we are clearing Thread identity in Session_End, and because of this - users were spontaneously losing authentication on thread.

So below is the corrected code that works.

Dim oHTTPContext As HttpContext = HttpContext.Current

Dim oSessionIdManager As New SessionIDManager
Dim sOldId As String = oSessionIdManager.GetSessionID(oHTTPContext)
Dim sNewId As String = oSessionIdManager.CreateSessionID(oHTTPContext)

Dim bIsRedir As Boolean = False
Dim bIsAdd As Boolean = False
oSessionIdManager.SaveSessionID(oHTTPContext, sNewId, bIsRedir, bIsAdd)

Dim oAppContext As HttpApplication = HttpContext.Current.ApplicationInstance

Dim oModules As HttpModuleCollection = oAppContext.Modules

Dim oSessionStateModule As SessionStateModule = _
  DirectCast(oModules.Get("Session"), SessionStateModule)

Dim oFields() As FieldInfo = _
  oSessionStateModule.GetType.GetFields(BindingFlags.NonPublic Or _
                                        BindingFlags.Instance)

Dim oStore As SessionStateStoreProviderBase = Nothing
Dim oRqIdField As FieldInfo = Nothing
Dim oRqItem As SessionStateStoreData = Nothing
Dim oRqLockIdField As FieldInfo = Nothing
Dim oRqStateNotFoundField As FieldInfo = Nothing

For Each oField As FieldInfo In oFields
    If (oField.Name.Equals("_store")) Then
        oStore = DirectCast(oField.GetValue(oSessionStateModule), _
                            SessionStateStoreProviderBase)
    End If
    If (oField.Name.Equals("_rqId")) Then
        oRqIdField = oField
    End If
    If (oField.Name.Equals("_rqLockId")) Then
        oRqLockIdField = oField
    End If
    If (oField.Name.Equals("_rqSessionStateNotFound")) Then
        oRqStateNotFoundField = oField
    End If
    If (oField.Name.Equals("_rqItem")) Then
        oRqItem = DirectCast(oField.GetValue(oSessionStateModule), _
                             SessionStateStoreData)
    End If
Next

If oStore IsNot Nothing Then

    Dim oLockId As Object = Nothing

    If oRqLockIdField IsNot Nothing Then
        oLockId = oRqLockIdField.GetValue(oSessionStateModule)
    End If

    If (oLockId IsNot Nothing) And (Not String.IsNullOrEmpty(sOldId)) Then
        oStore.ReleaseItemExclusive(oHTTPContext, sOldId, oLockId)
        oStore.RemoveItem(oHTTPContext, sOldId, oLockId, oRqItem)
    End If

    oRqStateNotFoundField.SetValue(oSessionStateModule, True)
    oRqIdField.SetValue(oSessionStateModule, sNewId)

End If

Answer 6

For MVC4 please have this code:

 System.Web.SessionState.SessionIDManager manager = new System.Web.SessionState.SessionIDManager();
            HttpContext Context = System.Web.HttpContext.Current;
            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)System.Web.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);