xen-kernel -- Hypervisor memory corruption due to x86 emulator flaw

The Xen Project reports:

Instructions with register operands ignore eventual segment
overrides encoded for them. Due to an insufficiently conditional
assignment such a bogus segment override can, however, corrupt a
pointer used subsequently to store the result of the instruction.
A malicious guest might be able to read sensitive data relating to
other guests, or to cause denial of service on the host. Arbitrary
code execution, and therefore privilege escalation, cannot be
excluded.