xen-tools -- virtio: unbounded memory allocation issue

The Xen Project reports:

A guest can submit virtio requests without bothering to wait for completion and is therefore not bound by virtqueue size...

A malicious guest administrator can cause unbounded memory allocation in QEMU, which can cause an Out-of-Memory condition in the domain running qemu. Thus, a malicious guest administrator can cause a denial of service affecting the whole host.

[source]