A NULL pointer dereference flaw was discovered in libvirt before version 5.0.0 in the way it gets interface information through the QEMU agent. An attacker in a guest VM can use this flaw to crash libvirtd and cause a denial of service.
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.
libvirt before 2.0.0 improperly disables password checking when the password on a VNC server is set to an empty string, which allows remote attackers to bypass authentication and establish a VNC session by connecting to the server.
The qemu implementation in libvirt before 1.3.0 and Xen allows local guest OS users to cause a denial of service (host disk consumption) by writing to stdout or stderr.
The virStorageVolCreateXML API in libvirt 1.2.14 through 1.2.19 allows remote authenticated users with a read-write connection to cause a denial of service (libvirtd crash) by triggering a failed unlink after creating a volume on a root_squash NFS pool.