/usr/share/check_mk/web/htdocs/defaults.py is in check-mk-config-icinga 1.1.12-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/check_mk/web/htdocs/../../modules/defaults
/usr/share/check_mk/web/htdocs/../../modules/defaults