The Xen Project has fixed four vulnerabilities in its widely used virtualization software. Two of the vulnerabilities could allow malicious virtual machine administrators to take over host servers. The vulnerabilities are the most serious kind for a hypervisor like Xen, which allows users to run multiple VMs on the same underlying hardware in a secure manner. The hypervisor is widely used by cloud computing providers and virtual private server hosting companies like Linode, which had to reboot some of its servers over the past few days to apply the new patches.”]