kernel is vulnerable to denial of service (DoS). The vulnerability exists as a missing error checking in the way page tables were handled in the Xen hypervisor implementation could allow a privileged guest user to cause the host, and the guests, to lock up.
docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/5.6_Technical_Notes/kernel.html#RHSA-2011-0833
downloads.avaya.com/css/P8/documents/100145416
rhn.redhat.com/errata/RHSA-2011-0833.html
wiki.xen.org/wiki/Security_Announcements#XSA-1_Host_crash_due_to_failure_to_correctly_validate_PV_kernel_execution_state.
access.redhat.com/errata/RHSA-2011:0833
access.redhat.com/security/updates/classification/#important