qemu/qemu_driver.c in libvirt before 6.0.0 mishandles the holding of a monitor job during a query to a guest agent, which allows attackers to cause a denial of service (API blockage).
https://www.mail-archive.com/debian-bugs-dist%40lists.debian.org/msg1730509.html
https://security-tracker.debian.org/tracker/CVE-2019-20485
https://libvirt.org/git/?p=libvirt.git%3Ba=commit%3Bh=a663a860819287e041c3de672aad1d8543098ecc