Hypervisor memory corruption due to x86 emulator flaw

ISSUE DESCRIPTION

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.

IMPACT

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.

VULNERABLE SYSTEMS

Xen 3.2.x and later are vulnerable. Xen 3.1.x and earlier have not been inspected.
Only x86 systems are vulnerable. ARM systems are not vulnerable.