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What are the Limitations When Working Under Medium Trust?

The more restrictive security sandbox imposed by medium trust curtails some operations that may have worked without issue when running in a full-trust environment. The following is a list of the known limitations when working in a medium-trust environment.

OLE DB Permissions are Not Granted By Default

The restriction on OleDBPermission affects any ASP.NET application that makes use of the OLE DB data provider support of ADO.NET, and is being migrated from a full-trust environment to a partial-trust environment.

The WebScheduleOleDbProvider™ control indirectly requires OleDbPermission because it communicates with OLE DB data sources (e.g., Microsoft® Access™ database file) through these Microsoft .NET Framework facilities. Consequently, it will not function in partial-trust environments unless your site administrator grants your application unrestricted OleDbPermission.

Your site administrator can add OleDbPermission to all medium-trust applications by editing the web_mediumtrust.config file. This file is located in the following path for .NET Framework 2.0:

%windir%\Microsoft.NET\Framework\v2.0.50727\Config

To grant unrestricted OleDbPermission, you must add the XML highlighted in the excerpt below to the web_mediumtrust.config file:

Note
Note:

If available, consider using the SqlClient data provider in partial trust environments, as it is more secure and scalable than OLE DB.

 
<SecurityClasses>
        ...
        <SecurityClass
          Name="OleDbPermission"
          Description="System.Data.OleDb.OleDbPermission, System.Data,
            Version=1.0.5000.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
</SecurityClasses>
    ...
        <IPermission
          class="WebPermission"
          version="1">
          <ConnectAccess>
                <URI uri="$OriginHost$"/>
          </ConnectAccess>
        <IPermission>
        <IPermission class="OleDbPermission"
          version="1">
          Unrestricted="true" />

          </PermissionSet>
        </NamedPermissionSets>
        ...

File I/O Permissions are Restricted to the Web Application’s Directory by Default

All external files which your Web application works with at run time will be constrained to the Web application’s directory.

Applications which load a preset dynamically at run time to restore the look and feel of the Ultimate UI for ASP.NET controls to a user’s custom preferences will need to deploy those preset files in their Web application’s directory.

If your application generates temporary files using the WebGridExcelExporter™ control with a DownloadMode of "Custom", it should intend to write those files in the Web application directory.

Where possible, it is recommended that you use IsolatedStorage instead of File I/O in Web applications running under partial trust.

Reflection is Permitted Only Against Public Members

Some properties may allow you to specify a .NET component, property, or field in your application. For example, the WebScheduleSqlClientProvider™ component allows you to specify the ConnectionID of an SqlConnection component at design time. At run time, such properties use late-binding (reflection) to connect with the named component, property, or field. Medium trust permits only late-binding to public members.

If the access qualifier on a .NET component, property, or field ("members") that you specify for these kinds of properties is the "protected", "private", "internal", or "family" keyword, then late-binding fails to connect. When running under partial trust, you must mark these members public or assign the property value directly.

For example, you have the choice of connecting the WebScheduleSqlClientProvider component to the SqlConnection in either of the following ways.

  • At design time, set the ConnectionID property to the name of your SqlConnection component (e.g., sqlConnection1) when sqlConnection1 has been marked with the "public" access qualifier.

  • At run time, during your Web Form’s Init event (after the InitializeComponents method has initialized your SqlConnection component), you can assign the SqlConnection component directly to the WebScheduleSqlClientProvider component’s Connection property.

In Visual Basic:

Me.WebScheduleSqlClientProvider1.Connection = Me.sqlConnection1

In C#:

this.WebScheduleSqlClientProvider1.Connection = this.sqlConnection1;