The MMIO instruction decoder in the Xen hypervisor in the Linux kernel 2.6.18 in Red Hat Enterprise Linux (RHEL) 5 allows guest OS users to cause a denial of service (32-bit guest OS crash) via vectors that trigger an unspecified instruction emulation.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A11430
https://bugzilla.redhat.com/show_bug.cgi?id=572971
http://www.vmware.com/security/advisories/VMSA-2011-0003.html
http://www.securityfocus.com/bid/39979
http://www.securityfocus.com/archive/1/516397/100/0/threaded
http://www.redhat.com/support/errata/RHSA-2010-0398.html
http://www.openwall.com/lists/oss-security/2010/05/07/1
http://support.avaya.com/css/P8/documents/100088287