Temporarily re-enabling CAS policy during migration

Over the last few weeks we’ve been looking at the changes to security policy in .NET 4, namely that security policy is now in the hands of the host and the operating system.

While we’ve looked at how to update code that implicitly uses CAS policy, loads assemblies from remote sources, and explicitly uses CAS policy, in applications of larger size it may not be practical to update all the code at once.  Similarly, you might be able to update the code in your application, but may rely on a third party assembly that is not yet updated for the changes in CAS policy.

If you do find yourself needing to re-enable CAS policy temporarily, in order to move a large code base to the new v4 security APIs bit by bit rather than all at once, or to use an assembly that you don’t control, there is a configuration switch that you can set in order to flip your process back into legacy CAS policy mode.

In order to temporarily enable legacy CAS policy in your process, you’ll need an .exe.config file for your application with the legacy security policy switch set in its runtime section.  So, if your application’s entry point is YourApp.exe, you’ll have next to it a YourApp.exe.config file.  (You can also use the app.config feature in your Visual Studio project).  The file should look like this for any release of the .NET Framework v4 after beta 1:



    <NetFx40_LegacySecurityPolicy enabled="true" />



In .NET 4 Beta 1, the switch has a slightly different name:



    <legacyCasPolicy enabled="true" />



One thing to note is that this switch must be set on the process-level.  So, if you’re using a third party control that uses CAS policy, you may well need to set the switch for both Visual Studio in devenv.exe.config and for your application itself.  That way the control will work both in the Visual Studio process during your development, as well as in your process at runtime.

Comments (4)
  1. Ted says:


    I just got a new computer and installed Windows 7 RC. I also installed Visual Studio 10.0.20506.1 Beta1 to test it.

    I moved my old Visual Studio 2005 projects, converted and then I get the error mentioned above.

    I added the line:

     <legacyCasPolicy enabled="true" />

    to the app.config in my project and also to devenv.exe.config.

    I did a rebuild of the project, restarted VS – but nothing helps. The same error.

    I also tried

     <NetFx40_LegacySecurityPolicy enabled="true" />

    no difference…

    Any ideas?

  2. ntrol will work both in the Visual Studio process during your development, as well as in your process at runtime

  3. To check the obvious, this config setting was within the <configuration><runtime> section of the config file correct?  Is your application a standalone .exe, or is it hosted by another app that might change the default config?


  4. Alechko says:


    I tried every switch you described and also all of them together. Doesn't help.

    I have a website in application pool configured as .NET 4.0.

    I also have .NET 4.0 applet which is hosted in ASP page in Object element.

    It was working for many years with full trust on policy configuration but at the moment we moved to .NET 4.0 it just stopped working and i still cannot do anything to solve it.

    I already removed any code from my applet just to leave it blank with single public property, but the DLL doesn't even downloaded to the client's PC (..assemblydl3 folder).

    Please help.


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