--- url.c       2018-01-30 16:19:20.307137284 -0800
+++ url-changed.c       2018-03-01 13:58:03.530696648 -0800
@@ -281,6 +281,9 @@
   /* Free all dynamic strings stored in the data->set substructure. */
   enum dupstring i;
   for(i = (enum dupstring)0; i < STRING_LAST; i++) {
+    if (data->set.str[i]) {
+      memset(data->set.str[i], 0, strlen(data->set.str[i]) *  sizeof (data->set.str[i][0]));
+    }
     Curl_safefree(data->set.str[i]);
   }