What is FullTrust? Do GAC’ed assemblies have FullTrust?

Manish Singh

14y13.7k.NET

Hi....

Ques: Hello all of you please explain What is FullTrust? Do GAC'ed assemblies have FullTrust?

2 Replies

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Anuja Pawar14y ago
Hi Manish,

Microsoft's ASP.NET web technology / language allows for web hosting companies to define trust levels, which dictate what operations are permitted by ASP.NET applications. A web hosting company can either use one of the preset trust levels - Full, High, Medium, Low, or Minimal - or can create a custom trust level.
Full trust is the default, allows ASP.NET applications to execute native code, to read from the Registry and Windows Event Log, and to read and write to files outside of the application's virtual directory. In short, with full trust one web application could delete the entire contents of another web application.

Although currently assemblies in the GAC receive FullTrust as a side effect of the GAC being on the local machine, from Whidbey beta 2 and beyond, being in the GAC will imply FullTrust on its own. A lot of the feedback wondered why we were doing this. Here's some of the reasoning:

Assemblies in the GAC build up the managed platform that all managed applications can run on. In order to build up a platform where any application, trusted or not, can run safely, it makes sense that you need to trust the assemblies making up that platform. If you don't trust an assembly enough for any code to be able to call into it, then the best place for it is probably not the GAC
By side-effect, assemblies in the GAC did already receive FullTrust. The only way that you could change this would be to either not grant MyComputer FullTrust, or create an exclusive code group that matched the strong name of the assembly and granted less trust.
Since you have to be an administrator in order to add an assembly to the GAC, it is already considered special from a security standpoint. For instance, strong name verification is skipped for assemblies that are loaded from the GAC.
If an application is hosting the CLR, it has the ability to protect itself from assemblies it doesn't trust to load. For instance, SQL Server 2005 does not allow the Windows Forms library to load. Applications can provide an AppDomainManager and HostSecurityManager in order to disallow some assemblies from loading, or to tweak their grant sets.
Assembly-level declarative security still works to reduce the grant set, so if you really need it, there is a knob you can turn to reduce the granted permissions of an assembly stored in the GAC.
Based upon the assumption that GACed assemblies are receiving FullTrust, tools such as NGEN can have simpler code paths around security. And reducing complexity in code paths that involve security helps to reduce the risk of bugs, which is a very good thing.
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Satyapriya Nayak14y ago
Hi Manish,

Before the .NET Framework existed, Windows had two levels of trust for downloaded code. This old model was a binary trust model. You only had two choices: Full Trust, and No Trust. The code could either do anything you could do, or it wouldn't run at all.

The permission sets in .NET include FullTrust, SkipVerification, Execution, Nothing, LocalIntranet, Internet and Everything. Full Trust Grants unrestricted permissions to system resources. Fully trusted code run by a normal, nonprivileged user cannot do administrative tasks, but can access any resources the user can access, and do anything the user can do. From a security standpoint, you can think of fully trusted code as being similar to native, unmanaged code, like a traditional ActiveX control.

GAC assemblies are granted FullTrust. In v1.0 and 1.1, the fact that assemblies in the GAC seem to always get a FullTrust grant is actually a side effect of the fact that the GAC lives on the local machine.? If anyone were to lock down the security policy by changing the grant set of the local machine to something less than FullTrust, and if your assembly did not get extra permission from some other code group, it would no longer have FullTrust even though it lives in the GAC.

Refer

http://kyapoocha.com/what-is-fulltrust-do-gac%E2%80%99ed-assemblies-have-fulltrust.html

Thanks
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