Some HTTP/2 implementations are vulnerable to a settings flood, potentially leading to a denial of service. The attacker sends a stream of SETTINGS frames to the peer. Since the RFC requires that the peer reply with one acknowledgement per SETTINGS frame, an empty SETTINGS frame is almost equivalent in behavior to a ping. Depending on how efficiently this data is queued, this can consume excess CPU, memory, or both.
https://www.synology.com/security/advisory/Synology_SA_19_33
https://www.debian.org/security/2019/dsa-4520
https://www.debian.org/security/2019/dsa-4508
https://usn.ubuntu.com/4308-1/
https://support.f5.com/csp/article/K50233772?utm_source=f5support&%3Butm_medium=RSS
https://support.f5.com/csp/article/K50233772
https://security.netapp.com/advisory/ntap-20190823-0005/
https://seclists.org/bugtraq/2019/Sep/18
https://seclists.org/bugtraq/2019/Aug/43
https://seclists.org/bugtraq/2019/Aug/24
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-2020:0727
https://access.redhat.com/errata/RHSA-2019:4352
https://access.redhat.com/errata/RHSA-2019:4045
https://access.redhat.com/errata/RHSA-2019:4042
https://access.redhat.com/errata/RHSA-2019:4041
https://access.redhat.com/errata/RHSA-2019:4040
https://access.redhat.com/errata/RHSA-2019:4021
https://access.redhat.com/errata/RHSA-2019:4020
https://access.redhat.com/errata/RHSA-2019:4019
https://access.redhat.com/errata/RHSA-2019:4018
https://access.redhat.com/errata/RHSA-2019:3892
https://access.redhat.com/errata/RHSA-2019:2955
https://access.redhat.com/errata/RHSA-2019:2939
https://access.redhat.com/errata/RHSA-2019:2925
https://access.redhat.com/errata/RHSA-2019:2861
https://access.redhat.com/errata/RHSA-2019:2796
https://access.redhat.com/errata/RHSA-2019:2766
http://seclists.org/fulldisclosure/2019/Aug/16
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00032.html
http://lists.opensuse.org/opensuse-security-announce/2019-09/msg00031.html