I applied the patch from here: https://www.drupal.org/sa-core-2018-002 to my Drupal 7.53 site. I can't do a full upgrade as it might break stuff. The patch caused the following error as found in my httpd log file.
PHP Fatal error: require_once(): Failed opening required '/var/www/xxxxx/includes/request-sanitizer.inc' (include_path='.:/usr/share/pear') in /var/www/xxxx/includes/bootstrap.inc on line 2622
What could be wrong? The file does exist in that directory and this patch worked fine on another site I patched.
FYI, my server is on PHP 5.3.6