A CSRF issue was discovered in DAViCal through 1.1.8. If an authenticated user visits an attacker-controlled webpage, the attacker can send arbitrary requests in the name of the user to the application. If the attacked user is an administrator, the attacker could for example add a new admin user.
https://www.debian.org/security/2019/dsa-4582
https://seclists.org/bugtraq/2019/Dec/30
https://lists.debian.org/debian-lts-announce/2019/12/msg00016.html
https://gitlab.com/davical-project/davical/blob/master/ChangeLog
http://seclists.org/fulldisclosure/2019/Dec/19
http://seclists.org/fulldisclosure/2019/Dec/18