Xen is an open source Hypervisor using a microkernel design. This allows to create muiltiple guest virtual machine.
Xen just released two patches to address various security vulnerabilities and it is highly recommended that you update as soon as possible.
They may release more security updates in near future so keep an eye on the future security updates.
 Information leak via internal x86 system device emulation
 Information leak through version information hypercall