Please Install the Updated Packages.
The xen packages contain administration tools and the xend service for managing the kernel-xen kernel for virtualization on Red Hat Enterprise Linux. A flaw was found in the way libxc, the Xen control library, handled excessively large kernel and ramdisk images when starting new guests. A privileged guest user in a para-virtualized guest (a DomU) could create a crafted kernel or ramdisk image that, when attempting to use it during guest start, could result in an out-of-memory condition in the privileged domain (the Dom0). (CVE-2012-4544) Red Hat would like to thank the Xen project for reporting this issue. All users of xen are advised to upgrade to these updated packages, which correct this issue. After installing the updated packages, the xend service must be restarted for this update to take effect.
xen on CentOS 5
Updated on 2015-03-25