A vulnerability was found in Apache HTTP Server 2.4.34 to 2.4.38. When HTTP/2 was enabled for a http: host or H2Upgrade was enabled for h2 on a https: host, an Upgrade request from http/1.1 to http/2 that was not the first request on a connection could lead to a misconfiguration and crash. Server that never enabled the h2 protocol or that only enabled it for https: and did not set "H2Upgrade on" are unaffected by this issue.
https://www.oracle.com/technetwork/security-advisory/cpuoct2019-5072832.html
https://www.oracle.com/technetwork/security-advisory/cpujul2019-5072835.html
https://www.oracle.com/security-alerts/cpuapr2020.html
https://usn.ubuntu.com/4113-1/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03950en_us
https://support.f5.com/csp/article/K44591505
https://security.netapp.com/advisory/ntap-20190617-0002/
https://httpd.apache.org/security/vulnerabilities_24.html
https://access.redhat.com/errata/RHSA-2019:3935
https://access.redhat.com/errata/RHSA-2019:3933
https://access.redhat.com/errata/RHSA-2019:3932
http://www.securityfocus.com/bid/107665
http://www.openwall.com/lists/oss-security/2019/04/02/2
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00084.html
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00061.html
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00051.html