LemonLDAP::NG before 1.9.20 has an XML External Entity (XXE) issue when submitting a notification to the notification server. By default, the notification server is not enabled and has a "deny all" rule.
https://www.calypt.com/blog/index.php/cve-2019-13031-xxe-on-lemonldapng-2-0-5/
https://lists.debian.org/debian-lts-announce/2019/07/msg00003.html
https://gitlab.ow2.org/lemonldap-ng/lemonldap-ng/issues/1820