/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/ is in icingaweb2-module-monitoring 2.1.0-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/Action.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/HostAction.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/HostNote.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/Renderer/
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/Renderer/BackendAvailabilityNavigationItemRenderer.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/Renderer/MonitoringBadgeNavigationItemRenderer.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/ServiceAction.php
/usr/share/icingaweb2/modules/monitoring/library/Monitoring/Web/Navigation/ServiceNote.php