The fix for CVE-2019-0199 was incomplete and did not address HTTP/2 connection window exhaustion on write in Apache Tomcat versions 9.0.0.M1 to 9.0.19 and 8.5.0 to 8.5.40 . By not sending WINDOW_UPDATE messages for the connection window (stream 0) clients were able to cause server-side threads to block eventually leading to thread exhaustion and a DoS.
https://www.synology.com/security/advisory/Synology_SA_19_29
https://www.oracle.com/technetwork/security-advisory/cpuoct2019-5072832.html
https://www.oracle.com/security-alerts/cpuoct2020.html
https://www.oracle.com/security-alerts/cpujan2020.html
https://www.oracle.com/security-alerts/cpuapr2020.html
https://www.oracle.com/security-alerts/cpuApr2021.html
https://www.debian.org/security/2020/dsa-4680
https://usn.ubuntu.com/4128-2/
https://usn.ubuntu.com/4128-1/
https://support.f5.com/csp/article/K17321505
https://security.netapp.com/advisory/ntap-20190625-0002/
https://access.redhat.com/errata/RHSA-2019:3931
https://access.redhat.com/errata/RHSA-2019:3929
http://www.securityfocus.com/bid/108874
http://lists.opensuse.org/opensuse-security-announce/2020-01/msg00013.html