FreeBSD -- Bhyve e82545 device emulation out-of-bounds write

Problem Description:
The e1000 network adapters permit a variety of modifications to an
Ethernet packet when it is being transmitted. These include the
insertion of IP and TCP checksums, insertion of an Ethernet VLAN
header, and TCP segmentation offload (“TSO”). The e1000 device model
uses an on-stack buffer to generate the modified packet header when
simulating these modifications on transmitted packets.
When checksum offload is requested for a transmitted packet, the
e1000 device model used a guest-provided value to specify the checksum
offset in the on-stack buffer. The offset was not validated for
certain packet types.
Impact:
A misbehaving bhyve guest could overwrite memory in the bhyve
process on the host, possibly leading to code execution in the host
context.
The bhyve process runs in a Capsicum sandbox, which (depending on
the FreeBSD version and bhyve configuration) limits the impact of
exploiting this issue.