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://access.redhat.com/errata/RHSA-2018:1396
https://access.redhat.com/errata/RHSA-2018:1929
https://bugzilla.redhat.com/show_bug.cgi?id=1550672
https://lists.debian.org/debian-lts-announce/2018/03/msg00018.html