In Apache HTTP Server 2.4 release 2.4.38 and prior, a race condition in mod_auth_digest when running in a threaded server could allow a user with valid credentials to authenticate using another username, bypassing configured access control restrictions.
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.debian.org/security/2019/dsa-4422
https://usn.ubuntu.com/3937-2/
https://usn.ubuntu.com/3937-1/
https://support.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03950en_us
https://security.netapp.com/advisory/ntap-20190423-0001/
https://seclists.org/bugtraq/2019/Apr/5
https://lists.debian.org/debian-lts-announce/2019/04/msg00008.html
https://httpd.apache.org/security/vulnerabilities_24.html
https://bugzilla.redhat.com/show_bug.cgi?id=1695020
https://access.redhat.com/errata/RHSA-2019:4126
https://access.redhat.com/errata/RHSA-2019:3935
https://access.redhat.com/errata/RHSA-2019:3933
https://access.redhat.com/errata/RHSA-2019:3932
https://access.redhat.com/errata/RHSA-2019:3436
https://access.redhat.com/errata/RHSA-2019:2343
http://www.securityfocus.com/bid/107668
http://www.openwall.com/lists/oss-security/2019/04/02/5
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