Security Advisor

Virtual Security

Virtualization heralds a brave new world of security. Here are a few things to keep in mind when it comes to securing a virtual infrastructure.

Within a short time, virtualization technology has moved from the labs of software testers and tinkerers into the mainstream of information technology. Microsoft, VMware, Citrix and other virtualization vendors are improving their technologies, and most companies have either started deploying virtual servers or are close to doing so.

One common challenge in maintaining virtualized environments is security. While many standard security guidelines apply to physical and virtual machines (VMs) alike, virtualization does present some unique security challenges. Here are some things to consider when creating a secure virtual IT infrastructure.

Of Hosts and Guests
Virtual security involves securing both the host and all VMs. Most of today's virtualization products use a specialized driver, called a hypervisor, to emulate the physical devices for each VM. Depending on the VM technology, the hypervisor may run in a regular operating system or in a minimal, special-purpose OS that's designed to run just the hypervisor. Microsoft's Hyper-V runs under Windows Server 2008 and thus requires a full operating system on the host computer. When a virtualization solution runs on a computer with a regular operating system, you should secure the host computer the same way you would secure any other server.

To keep its attack surface as small as possible, resist the temptation to install any services not required to host the VMs. Instead, install services like DNS and Exchange inside one of your VMs. Virtual hosts also need the same care and feeding as any other servers. This means you need to include them in your patching and anti-virus plans.

Stripped Down
Some virtualization products like VMware's ESX server use an operating system consisting only of the hypervisor and a management interface. This means that you won't need to worry about anti-virus software or even be tempted to install unnecessary services.

Securing virtualization hosts is important, but VMs exist in their own world, oblivious to how you've configured the host or which software it's running. As far as the OS and applications are concerned, each VM is just another computer. As a result, a VM faces the same threats as a physical server.

Keep Track of Virtual Servers
The most overlooked security threat from virtualization stems from the uncontrolled proliferation of VMs. Adding a new virtual server to your network is much cheaper and easier than deploying a new physical server, especially as it doesn't involve convincing managers to sign off on buying new hardware. The result is often a proliferation of haphazardly managed virtual servers.

Once an organization starts to embrace virtualization, there's soon a plethora of VMs on the network. Some of them are turned on, some of them turned off and others are forgotten. When your company needs a server for a short-term project, it's often deployed as a virtual server. Then, when the server is no longer needed, it's typically powered off, but the files that comprise its configuration and virtual hard disk aren't deleted. If such a VM is turned on at a later time, it has likely missed several patch cycles and thus may be vulnerable to attacks.

To avoid such a threat and to stay in control of virtual servers in your organization, a combination of policies and monitoring tools is required. Make sure your security policy contains rules about who can install new virtual servers, what configuration guidelines must be followed and how virtual servers are decommissioned. The decommissioning procedure should go beyond deleting the VM files and include steps for tracking which VMs actually exist in your organization and who is responsible for each of them.

Even though your infrastructure may be virtual, the security threats to it are real. Fortunately, by making only a few adjustments to your security strategy and procedures, you can effectively protect your virtual infrastructure.

About the Author

Joern Wettern, Ph.D., MCSE, MCT, Security+, is the owner of Wettern Network Solutions, a consulting and training firm. He has written books and developed training courses on a number of networking and security topics. In addition to helping companies implement network security solutions, he regularly teaches seminars and speaks at conferences worldwide.


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