The Apache HTTP Server 2.4.18 through 2.4.20, when mod_http2 and mod_ssl are enabled, does not properly recognize the "SSLVerifyClient require" directive for HTTP/2 request authorization, which allows remote attackers to bypass intended access restrictions by leveraging the ability to send multiple requests over a single connection and aborting a renegotiation.
https://security.netapp.com/advisory/ntap-20180601-0001/
https://security.gentoo.org/glsa/201610-02
https://github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2
https://access.redhat.com/errata/RHSA-2016:1420
http://www.securitytracker.com/id/1036225
http://www.securityfocus.com/bid/91566
http://www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html
http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
http://www.openwall.com/lists/oss-security/2016/07/05/5
http://www.apache.org/dist/httpd/CHANGES_2.4
http://seclists.org/fulldisclosure/2016/Jul/11
http://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html