The mod_headers module in the Apache HTTP Server 2.2.22 allows remote attackers to bypass "RequestHeader unset" directives by placing a header in the trailer portion of data sent with chunked transfer coding. NOTE: the vendor states "this is not a security issue in httpd as such."
https://support.apple.com/HT205219
https://support.apple.com/HT204659
https://security.gentoo.org/glsa/201504-03
https://httpd.apache.org/security/vulnerabilities_24.html
https://h20564.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c04832246
https://access.redhat.com/errata/RHSA-2015:2660
https://access.redhat.com/errata/RHSA-2015:2659
http://www.ubuntu.com/usn/USN-2523-1
http://www.securityfocus.com/bid/66550
http://www.oracle.com/technetwork/topics/security/linuxbulletinjan2016-2867209.html
http://www.oracle.com/technetwork/topics/security/cpujul2015-2367936.html
http://www.oracle.com/technetwork/topics/security/cpujan2016-2367955.html
http://www.oracle.com/technetwork/topics/security/cpujan2015-1972971.html
http://www.oracle.com/technetwork/topics/security/bulletinjan2015-2370101.html
http://www.mandriva.com/security/advisories?name=MDVSA-2014:174
http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/proxy/mod_proxy_http.c
http://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x/CHANGES
http://rhn.redhat.com/errata/RHSA-2016-0062.html
http://rhn.redhat.com/errata/RHSA-2016-0061.html
http://rhn.redhat.com/errata/RHSA-2015-1249.html
http://rhn.redhat.com/errata/RHSA-2015-0325.html
http://marc.info/?l=bugtraq&m=144493176821532&w=2
http://marc.info/?l=bugtraq&m=143403519711434&w=2
http://marc.info/?l=apache-httpd-dev&m=139636309822854&w=2
http://lists.apple.com/archives/security-announce/2015/Sep/msg00004.html
http://lists.apple.com/archives/security-announce/2015/Apr/msg00001.html