If an HTTP/2 client connecting to Apache Tomcat 10.0.0-M1 to 10.0.0-M7, 9.0.0.M1 to 9.0.37 or 8.5.0 to 8.5.57 exceeded the agreed maximum number of concurrent streams for a connection (in violation of the HTTP/2 protocol), it was possible that a subsequent request made on that connection could contain HTTP headers - including HTTP/2 pseudo headers - from a previous request rather than the intended headers. This could lead to users seeing responses for unexpected resources.
https://www.oracle.com/security-alerts/cpuApr2021.html
https://www.debian.org/security/2021/dsa-4835
https://security.netapp.com/advisory/ntap-20201016-0007/
https://lists.debian.org/debian-lts-announce/2020/10/msg00019.html
http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00021.html
http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00002.html