Some HTTP/2 implementations are vulnerable to unconstrained interal data buffering, potentially leading to a denial of service. The attacker opens the HTTP/2 window so the peer can send without constraint; however, they leave the TCP window closed so the peer cannot actually write (many of) the bytes on the wire. The attacker then sends a stream of requests for a large response object. Depending on how the servers queue the responses, this can consume excess memory, CPU, or both.
https://www.synology.com/security/advisory/Synology_SA_19_33
https://www.oracle.com/technetwork/security-advisory/cpuoct2019-5072832.html
https://www.oracle.com/security-alerts/cpuapr2020.html
https://www.debian.org/security/2019/dsa-4509
https://usn.ubuntu.com/4113-1/
https://support.f5.com/csp/article/K02591030?utm_source=f5support&%3Butm_medium=RSS
https://support.f5.com/csp/article/K02591030
https://security.netapp.com/advisory/ntap-20190905-0003/
https://security.netapp.com/advisory/ntap-20190823-0005/
https://security.netapp.com/advisory/ntap-20190823-0003/
https://security.gentoo.org/glsa/201909-04
https://seclists.org/bugtraq/2019/Aug/47
https://kc.mcafee.com/corporate/index?page=content&id=SB10296
https://kb.cert.org/vuls/id/605641/
https://github.com/Netflix/security-bulletins/blob/master/advisories/third-party/2019-002.md
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-2019:2955
https://access.redhat.com/errata/RHSA-2019:2950
https://access.redhat.com/errata/RHSA-2019:2949
https://access.redhat.com/errata/RHSA-2019:2946
https://access.redhat.com/errata/RHSA-2019:2939
https://access.redhat.com/errata/RHSA-2019:2925
https://access.redhat.com/errata/RHSA-2019:2893
http://www.openwall.com/lists/oss-security/2019/08/15/7
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00032.html
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00031.html
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00004.html