Improving Web Application Security: Threats and - CGISecurity

Chapter 7: Building Secure Assemblies 169Validate Array BoundsIf you pass input to an unmanaged API using an array, check that the managedwrapper verifies that the capacity of the array is not exceeded.Check File Path LengthsIf the unmanaged API accepts a file name and path, check that it does not exceed260 characters. This limit is defined by the Win32 MAX_PATH constant. It is verycommon for unmanaged code to allocate buffers of this length to manipulate filepaths.Note Directory names and registry keys can only be a maximum of 248 characters long.DelegatesCompile Unmanaged Code With the /GS SwitchIf you own the unmanaged code, compile it using the /GS switch to enable stackprobes to help detect buffer overflows. For more information about the /GS switch,see Microsoft Knowledge Base article 325483, “WebCast: Compiler Security Checks:The -GS compiler switch.”Inspect Unmanaged Code for Dangerous APIsIf you have access to the source code for the unmanaged code that you are calling,you should subject it to a thorough code review, paying particular attention toparameter handling to ensure that buffer overflows are not possible and that it doesnot use potentially dangerous APIs. For more information see Chapter 21, “CodeReview.”Delegates are the managed equivalent of type safe function pointers and are used bythe .NET Framework to support events. The delegate object maintains a reference to amethod, which is called when the delegate is invoked. Events allow multiplemethods to be registered as event handlers. When the event occurs, all event handlersare called.Do Not Accept Delegates from Untrusted SourcesIf your assembly exposes a delegate or an event, be aware that any code canassociate a method with the delegate and you have no advance knowledge ofwhat the code does. The safest policy is not to accept delegates from untrustedcallers. If your assembly is strong named and does not include theAllowPartiallyTrustedCallersAttribute, only Full Trust callers can pass youa delegate.