The virConnectGetDomainCapabilities() libvirt API, versions 4.x.x before 4.10.1 and 5.x.x before 5.4.1, accepts an "emulatorbin" argument to specify the program providing emulation for a domain. Since v1.2.19, libvirt will execute that program to probe the domain's capabilities. Read-only clients could specify an arbitrary path for this argument, causing libvirtd to execute a crafted executable with its own privileges.
{
    "availability": "No subscription required",
    "binaries": [
        {
            "binary_name": "libvirt-bin",
            "binary_version": "1.3.1-1ubuntu10.27"
        },
        {
            "binary_name": "libvirt-dev",
            "binary_version": "1.3.1-1ubuntu10.27"
        },
        {
            "binary_name": "libvirt0",
            "binary_version": "1.3.1-1ubuntu10.27"
        }
    ]
}
          {
    "availability": "No subscription required",
    "binaries": [
        {
            "binary_name": "libnss-libvirt",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-bin",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-clients",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon-driver-storage-gluster",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon-driver-storage-rbd",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon-driver-storage-sheepdog",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon-driver-storage-zfs",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-daemon-system",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-dev",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-sanlock",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt-wireshark",
            "binary_version": "4.0.0-1ubuntu8.12"
        },
        {
            "binary_name": "libvirt0",
            "binary_version": "4.0.0-1ubuntu8.12"
        }
    ]
}