Index: /trunk/src/VBox/Main/src-client/DisplayImpl.cpp
===================================================================
--- /trunk/src/VBox/Main/src-client/DisplayImpl.cpp	(revision 83621)
+++ /trunk/src/VBox/Main/src-client/DisplayImpl.cpp	(revision 83622)
@@ -3101,4 +3101,10 @@
 int Display::i_handleVHWACommandProcess(int enmCmd, bool fGuestCmd, VBOXVHWACMD RT_UNTRUSTED_VOLATILE_GUEST *pCommand)
 {
+    /* bugref:9691 Disable the legacy VHWA interface.
+     * Keep the host commands enabled because they are needed when an old saved state is loaded.
+     */
+    if (fGuestCmd)
+        return VERR_NOT_IMPLEMENTED;
+
     unsigned id = (unsigned)pCommand->iDisplay;
     if (id >= mcMonitors)