An h2c direct connection to Apache Tomcat 10.0.0-M1 to 10.0.0-M6, 9.0.0.M5 to 9.0.36 and 8.5.1 to 8.5.56 did not release the HTTP/1.1 processor after the upgrade to HTTP/2. If a sufficient number of such requests were made, an OutOfMemoryException could occur leading to a denial of service.
https://www.oracle.com/security-alerts/cpuoct2020.html
https://www.oracle.com/security-alerts/cpujan2022.html
https://www.oracle.com/security-alerts/cpujan2021.html
https://www.oracle.com/security-alerts/cpuApr2021.html
https://www.oracle.com//security-alerts/cpujul2021.html
https://www.debian.org/security/2020/dsa-4727
https://usn.ubuntu.com/4596-1/
https://security.netapp.com/advisory/ntap-20200724-0003/
https://lists.debian.org/debian-lts-announce/2020/07/msg00017.html
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00088.html
http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00084.html