In Phusion Passenger before 5.1.0, a known /tmp filename was used during passenger-install-nginx-module execution, which could allow local attackers to gain the privileges of the passenger user.
https://github.com/phusion/passenger/commit/e5b4b0824d6b648525b4bf63d9fa37e5beeae441
https://github.com/phusion/passenger/blob/stable-5.1/CHANGELOG