agent/Core/Controller/SendRequest.cpp in Phusion Passenger before 4.0.60 and 5.0.x before 5.0.22, when used in Apache integration mode or in standalone mode without a filtering proxy, allows remote attackers to spoof headers passed to applications by using an _ (underscore) character instead of a - (dash) character in an HTTP header, as demonstrated by an X_User header.

References

• https://nvd.nist.gov/vuln/detail/CVE-2015-7519
• phusion/passenger@ddb8ecc
• https://blog.phusion.nl/2015/12/07/cve-2015-7519/
• https://bugzilla.suse.com/show_bug.cgi?id=956281
• GHSA-fxwv-953p-7qpf
• https://lists.debian.org/debian-lts-announce/2018/06/msg00007.html
• http://lists.opensuse.org/opensuse-security-announce/2015-12/msg00024.html
• http://www.openwall.com/lists/oss-security/2015/12/07/1
• http://www.openwall.com/lists/oss-security/2015/12/07/2
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/passenger/CVE-2015-7519.yml
• https://web.archive.org/web/20220327073056/https://www.puppet.com/security/cve/passenger-dec-2015-security-fixes