Improving Web Application Security: Threats and - CGISecurity

Chapter 8: Code Access Security in Practice 195RequestMinimumYou can use SecurityAction.RequestMinimum method along with declarativepermission attributes to specify the minimum set of permissions your assemblyneeds to run. For example, if your assembly needs to access the registry, but onlyneeds to retrieve configuration data from a specific key, use an attribute similar to thefollowing:[assembly: RegistryPermissionAttribute(SecurityAction.RequestMinimum,Read=@"HKEY_LOCAL_MACHINE\SOFTWARE\YourApp")]If you know up front that your code will run in a full trust environment and will begranted the full set of unrestricted permissions, using RequestMinimum is lessimportant. However, it is good practice to specify your assembly’s permissionrequirements.Note Permission attributes accept a comma-delimited list of properties and property values afterthe mandatory constructor arguments. These are used to initialize the underlying permission object.A quick way to find out what property names are supported is to use Ildasm.exe on the assemblythat contains the permission attribute type.RequestOptionalIf you use SecurityAction.RequestOptional method, no other permissions exceptthose specified with SecurityAction.RequestMinimum andSecurityAction.RequestOptional will be granted to your assembly, even if yourassembly would otherwise have been granted additional permissions by code accesssecurity policy.RequestRefusedSecurityAction.RequestRefuse allows you to make sure that your assembly cannotbe granted permissions by code access security policy that it does not require. Forexample, if your assembly does not call unmanaged code, you could use thefollowing attribute to ensure code access security policy does not grant yourassembly the unmanaged code permission.[assembly: SecurityPermissionAttribute(SecurityAction.RequestRefuse,UnmanagedCode=true)]