Any OpenStack installation that hosts services and VMs for several customers poses a challenge for the security-conscious admin. Hardening the overall system can turn the porous walls into a fortress – but you’ll need more than a little mortar.
One of the biggest concerns about virtualization is that an attacker could succeed in breaking out of the virtual machine (VM) and thus gain access to the resources of the physical host. The security of virtual systems thus hinges on the ability to isolate resources of the various VMs on the same server.
A simple thought experiment shows how important it is that the boundaries of VM and host are not blurred. Assume you have a server that hosts multiple VMs that all belong to the same customer. In this scenario, a problem occurs if a user manages to break out from a VM and gain direct access to the server: In the worst case, the attacker now has full access to the VMs on the host and can access sensitive data at will, or even set up booby traps to fish for even more information.
To gain unauthorized access, attackers need to negotiate multiple obstacles: First, they must gain access to the VM itself. If all VMs belong to the same customer and the same admins regularly maintain them, this risk is minimized, but it cannot be ruled out. In the second step, an attacker needs to negotiate the barrier between the VM and the host. Technologies such as SELinux can help to minimize the risks of an attacker crossing the VM barrier.
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