In Horde Groupware 5.2.19-5.2.22, there is XSS via the URL field in a "Calendar -> New Event" action.
https://lists.debian.org/debian-lts-announce/2020/08/msg00049.html
https://github.com/horde/kronolith/commit/09d90141292f9ec516a7a2007bf828ce2bbdf60d