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 QEMU emulated the e1000 network interface card when the host was configured to accept jumbo network frames, and a fully-virtualized guest using the e1000 emulated driver was not. A remote attacker could use this flaw to crash the guest or, potentially, execute arbitrary code with root privileges in the guest. (CVE-2012-6075)
All users of xen are advised to upgrade to these updated packages, which correct this issue. After installing the updated packages, all running fully-virtualized guests must be restarted for this update to take effect.