Unbound before 1.10.1 has an infinite loop via malformed DNS answers received from upstream servers.
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00067.html
http://lists.opensuse.org/opensuse-security-announce/2020-06/msg00069.html
https://lists.debian.org/debian-lts-announce/2021/02/msg00017.html
https://security.FreeBSD.org/advisories/FreeBSD-SA-20:19.unbound.asc
https://usn.ubuntu.com/4374-1/