Why Azure Web Role by default runs in the Full Trust?

Question

When I create an Azure ASP.NET application, by default .NET trust level is Full trust. I always change it to Windows Azure partial trust which is similar to ASP.NET's medium trust level.

You can do it either by using GUI when you select Properties on the Role or by setting enableNativeCodeExecution to false in the definition file (.csdef) just like below:

<WebRole name="ServiceRuntimeWebsite" enableNativeCodeExecution="false">

As a security conscious developer I want by default to run my application in partial trust mode that provides a higher level of security. If I need to use something like Reflection or P/Invoke, as a developer I want to make the decision to lower that trust level by myself.

I'm sure there's a reason why Microsoft decided to use Full trust as a default .NET trust level, I just fail to see it. If you know the reason, or you think you know it, please let me know.

Answer 1

Full trust is not only required for P/Invoke for .NET reflection as well. As a bottom line result, nearly all moderately sized apps need full trust because nearly all widespread libraries need it too (NHibernate for example). Actually, I have been asking from the exact opposite question on the Azure forums too.

Answer 2

The issue of full or partial trust pertains to the environment in which your application runs. The more control and/or "ownership" of the environment and assemblies you have, the more acceptable it is to have full-trust settings.

For example, if you create an Azure web site (July 2012 capability) and, mimicking wordpress or Umbraco, your web site allows arbitrary assembly plugins to be downloaded and installed, then it is important to have a partially-trusted environment. It is possible that one of the plugins downloaded and executed, which you don't control or own, contains malware. Not only does this impact the security and stability of your web site, but some may argue it impacts other (multi-tenant) hosted web-sites which have no relation to yours.

Certainly your web site will rely on 3rd party libraries, such as Log4Net or StructureMap, but those are extremely well-known and vetted libraries that are not in question regarding their security impact. Ergo, if you are running an Azure web-role (a much less "multi-tenant" type affair) and you are merely running such "trusted" 3rd party apps, then there really is not an issue with running as full-trust.

Answer 3

Yes, unfortunately it is still very hard (if not impossible) to write large .NET apps that run in partial trust.

We need much better technology and tools (like CAS.NET)

Answer 4

Because Medium Trust is now officially obsolete. If you start a new web project in Visual Studio, it already requires Full Trust (and doesn't work partial trust). Microsoft says: Do not depend on Medium Trust, instead, use Full Trust, and isolate untrusted applications in separate application pools.

Sources:

Stackoverflow answer: Quoted response ASP.NET team

Microsoft: ASP.NET Partial Trust does not guarantee application isolation

Microsoft: ASP.NET web development best practices