Index: /trunk/src/VBox/Main/src-server/MachineImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 35837)
+++ /trunk/src/VBox/Main/src-server/MachineImpl.cpp	(revision 35838)
@@ -4423,5 +4423,7 @@
     {
         IMedium *pIMedium(sfaMedia[i]);
-        Medium *pMedium = static_cast<Medium*>(pIMedium);
+        ComObjPtr<Medium> pMedium = static_cast<Medium*>(pIMedium);
+        if (pMedium.isNull())
+            return setError(E_INVALIDARG, "The given medium pointer %d is invalid", i);
         AutoCaller mediumAutoCaller(pMedium);
         if (FAILED(mediumAutoCaller.rc())) return mediumAutoCaller.rc();