The http parser in Phusion Passenger 6.0.21 through 6.0.25 before 6.0.26 allows a denial of service during parsing of a request with an invalid HTTP method.
https://www.phusionpassenger.com/support
https://github.com/phusion/passenger/releases/tag/release-6.0.26
https://github.com/phusion/passenger/compare/release-6.0.25...release-6.0.26
https://github.com/phusion/passenger/commit/bb15591646687064ab2d578d5f9660b2a4168017