_dbus_header_cache_known_nonexistent (DBusHeader    *header,
                                      int            field)
{
  _dbus_assert (field <= DBUS_HEADER_FIELD_LAST);

  return (header->fields[field].value_pos == _DBUS_HEADER_FIELD_VALUE_NONEXISTENT);
}

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.