CVE-2015-7519: Header overwriting

It is possible in some cases, for clients to overwrite headers set by the server, resulting in a medium level security issue. Passenger 5 uses an SCGI-inspired format to pass headers to Ruby/Python applications, while Passenger 4 uses an SCGI-inspired format to pass headers to all applications. This implies a conversion to UPPER_CASE_WITH_UNDERSCORES whereby the difference between characters like ‘-’ and ‘_’ is lost. See “Affected use-cases” in provided link to establish wether one particular application is affected.