Improving Web Application Security: Threats and - CGISecurity

208 Part III: Building Secure Web ApplicationsConstraining Event Logging CodeIf you want to constrain the actions of event log wrapper code — perhaps codewritten by another developer or development organization — you can use declarativeattributes together with SecurityAction.PermitOnly as shown in the followingexample.The following attribute ensures that the WriteToLog method and any methods it callscan only access the local computer’s event log and cannot delete event logs or eventsources. These operations are not permitted byEventLogPermissionAccess.Instrument.[EventLogPermission(SecurityAction.PermitOnly,MachineName=".",PermissionAccess=EventLogPermissionAccess.Instrument)]public static void WriteToLog( string message )To enforce read-only access to existing logs, use EventLogPermissionAccess.Browse.Requesting EventLogPermissionTo document the permission requirements of your code, and to ensure that yourassembly cannot load if it is granted insufficient event log access by code accesssecurity policy, add an assembly level EventLogPermissionAttribute withSecurityAction.RequestMinimum as shown in the following example.// This attribute indicates that your code requires the ability to access the// event logs on the local machine only (".") and needs instrumentation access// which means it can read or write to existing logs and create new event sources// and event logs[assembly: EventLogPermissionAttribute(SecurityAction.RequestMinimum,MachineName=".",PermissionAccess=EventLogPermissionAccess.Instrument)]RegistryCode that accesses the registry by using the Microsoft.Win32.Registry class must begranted the RegistryPermission by code access security policy. This permission typecan be used to constrain registry access to specific keys and sub keys, and can alsocontrol code’s ability to read, write, or create registry keys and named values.