Index: wp-admin/update-core.php
===================================================================
--- wp-admin/update-core.php	(revision 15473)
+++ wp-admin/update-core.php	(working copy)
@@ -372,6 +372,11 @@
 
 $action = isset($_GET['action']) ? $_GET['action'] : 'upgrade-core';
 
+if( ! in_array( $action, array( 'do-plugin-upgrade', 'upgrade-core', 'do-core-upgrade', 'do-core-reinstall', 'do-theme-upgrade' ) ) ) {
+	wp_redirect( admin_url( 'update-core.php' ) );
+	exit;
+}
+
 $upgrade_error = false;
 if ( 'do-plugin-upgrade' == $action && !isset($_GET['plugins']) && !isset($_POST['checked']) ) {
 	$upgrade_error = true;