70-340 Implementing Security for Applications with Microsoft Visual C# .NET Exam Review

Demo Question 19.

You are an application developer for EliteCertify.com. You develop a library assembly that contains diagnostic utility classes. This library assembly is installed in the global assembly cache on all client computers on EliteCertify 's network. You develop a Windows Forms application that calls the library assembly. You successfully test the application on your computer, and then you deploy the application to a Web folder on the intranet. Further testing reveals that when you run this application from the intranet, a SecurityException exception is thrown when the application is loading. You need to correct the problem that is causing the SecurityException exception. What should you do?

A. Add the following code segment to the library assembly. [assembly: AllowPartialTrustedCallers]
B. Add the following code segment to the Windows Forms application assembly. [assembly: AllowPartiallyTrustedCallers]
C. Add the following code segment to the library assembly. [assembly: PermissionSet(SecurityAction.RequestOptional, Name = "Loca
D. Add the following code segment to the Windows Forms application assembly. [assembly: PermissionSet(SecurityAction.RequestMinimum, Name = "Local


Display Answer

Answer: D

Explanation: .NET permissions are grouped into NamedPermissionSets. The platform includes the following non-modifiable built-in sets: Nothing, Execution, FullTrust, Internet, LocalIntranet, SkipVerification. The FullTrust set is a special case, as it declares that this code does not have any restrictions and passes any permission check, even for custom permissions. By default, all local code (found in the local computer directories) is granted this privilege. The above fixed permission sets can be demanded instead of regular permissions: [assembly:PermissionSetAttribute( SecurityAction.RequestMinimum, Name="LocalIntranet")] Here is a summary of some facts or rules: 7. If you want to restrict the permissions given to an assembly to only those contained in the associated permission set, you must tick the code group option "The policy level will only have the permissions from the permission set associated with this code group". Otherwise what is granted to the assembly is the permissions of the particular assocated permission set plus permissions of the associated permission set of the inherited code group ("All_Code" group). 8. All assemblies must be given "Enable assembly execution" security permission so that it can be run or launched. 9. Permissions included in an assembly's associated permission set that are above the logged-in user's previllege will not be granted. 10. A strongly named assembly can only be called by a fully-trusted caller, unless this assembly states AllowPartiallyTrustedCallers. When you use this attribute, it means that you have fully reviewed your code and there is no security flaw that may be used by luring attackers - such as a improperly used Assert. Not all system assemblies are marked with this attribute. You can look at the assembly's manifest to see whether it has that attribute. 11. However, an assembly belonging to the root "All_Code" code group can be called by partially-trusted callers, even if they are strongly named. This is probably because, if you don't impose a particular security control on an assembly, the runtime security thinks that this assembly is not extremely critical. 12. When you states AllowPartiallyTrustedCallers in an assembly, or let it stay in the "All_Code" code group, a permission-checking stack walk is still going to be triggered for every attempt to access any controlled resource. The only difference is if you improperly make a Assert you will make luring attacks possible.