hw/virtio/virtio.c in the Virtual Network Device (virtio-net) support in QEMU, when big or mergeable receive buffers are not supported, allows remote attackers to cause a denial of service (guest network consumption) via a flood of jumbo frames on the (1) tuntap or (2) macvtap interface.
hw/ide/core.c in QEMU does not properly restrict the commands accepted by an ATAPI device, which allows guest users to cause a denial of service or possibly have unspecified other impact via certain IDE commands, as demonstrated by a WIN_READ_NATIVE_MAX command to an empty drive, which triggers a divide-by-zero error and instance crash.