libvirt version before 4.2.0-rc1 is vulnerable to a resource exhaustion as a result of an incomplete fix for CVE-2018-5748 that affects QEMU monitor but now also triggered via QEMU guest agent.
https://www.debian.org/security/2018/dsa-4137
https://usn.ubuntu.com/3680-1/
https://lists.debian.org/debian-lts-announce/2018/03/msg00018.html
https://libvirt.org/git/?p=libvirt.git%3Ba=commit%3Bh=fbf31e1a4cd19d6f6e33e0937a009775cd7d9513
https://bugzilla.redhat.com/show_bug.cgi?id=1550672