In agent/Core/SpawningKit/Spawner.h in Phusion Passenger 5.1.10 (fixed in Passenger Open Source 5.1.11 and Passenger Enterprise 5.1.10), if Passenger is running as root, it is possible to list the contents of arbitrary files on a system by symlinking a file named REVISION from the application root folder to a file of choice and querying passenger-status --show=xml.

References

• https://nvd.nist.gov/vuln/detail/CVE-2017-16355
• phusion/passenger@4043718
• https://blog.phusion.nl/2017/10/13/passenger-security-advisory-5-1-11/
• https://seclists.org/bugtraq/2019/Mar/34
• https://www.debian.org/security/2019/dsa-4415
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/passenger/CVE-2017-16355.yml