qemu, xen-tools -- QEMU leak of uninitialized heap memory in rtl8139 device model

The Xen Project reports:

The QEMU model of the RTL8139 network card did not sufficiently
validate inputs in the C+ mode offload emulation. This results in
uninitialized memory from the QEMU process’s heap being leaked to
the domain as well as to the network.
A guest may be able to read sensitive host-level data relating to
itself which resides in the QEMU process.
Such information may include things such as information relating to
real devices backing emulated devices or passwords which the host
administrator does not intend to share with the guest admin.