An issue was discovered in Icinga2 before v2.12.0-rc1. The prepare-dirs script (run as part of the icinga2 systemd service) executes chmod 2750 /run/icinga2/cmd. /run/icinga2 is under control of an unprivileged user by default. If /run/icinga2/cmd is a symlink, then it will by followed and arbitrary files can be changed to mode 2750 by the unprivileged icinga2 user.
https://github.com/Icinga/icinga2/releases
https://github.com/Icinga/icinga2/pull/8045/commits/2f0f2e8c355b75fa4407d23f85feea037d2bc4b6
https://github.com/Icinga/icinga2/compare/v2.12.0-rc1...master