In Apache HTTP Server 2.4 releases 2.4.17 to 2.4.38, with MPM event, worker or prefork, code executing in less-privileged child processes or threads (including scripts executed by an in-process scripting interpreter) could execute arbitrary code with the privileges of the parent process (usually root) by manipulating the scoreboard. Non-Unix systems are not affected.
https://www.synology.com/security/advisory/Synology_SA_19_14
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://www.exploit-db.com/exploits/46676/
https://www.debian.org/security/2019/dsa-4422
https://usn.ubuntu.com/3937-1/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03950en_us
https://support.f5.com/csp/article/K32957101
https://security.netapp.com/advisory/ntap-20190423-0001/
https://security.gentoo.org/glsa/201904-20
https://seclists.org/bugtraq/2019/Apr/5
https://seclists.org/bugtraq/2019/Apr/16
https://httpd.apache.org/security/vulnerabilities_24.html
https://access.redhat.com/errata/RHSA-2019:1543
https://access.redhat.com/errata/RHSA-2019:1297
https://access.redhat.com/errata/RHSA-2019:1296
https://access.redhat.com/errata/RHSA-2019:0980
https://access.redhat.com/errata/RHSA-2019:0746
https://access.redhat.com/errata/RHBA-2019:0959
http://www.securityfocus.com/bid/107666
http://www.openwall.com/lists/oss-security/2019/07/26/7
http://www.openwall.com/lists/oss-security/2019/04/02/3
http://www.apache.org/dist/httpd/CHANGES_2.4.39
http://packetstormsecurity.com/files/152441/CARPE-DIEM-Apache-2.4.x-Local-Privilege-Escalation.html
http://packetstormsecurity.com/files/152415/Slackware-Security-Advisory-httpd-Updates.html
http://packetstormsecurity.com/files/152386/Apache-2.4.38-Root-Privilege-Escalation.html
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