I've written before about the huge benefits you can reap if you plan for large sitewide outages by giving yourself access to all the troubleshooting tools you'll need ahead of time. These days, that almost always includes access to a bevy of embedded management interfaces. These interfaces are common on devices like uninterruptible power supplies, network-attached power distribution units, blade chassis, and server hardware in the form of baseboard management controllers (BMCs). They can be an enormous help when you've had a full site failure or are remotely troubleshooting a huge range of problems.
However, they also can present an enormous risk if not protected properly.
Recently, US-CERT released a security advisory that explains the risks inherent with exposing Intelligent Platform Management Interface (IPMI) interfaces to unsecured networks. IPMI is an API standard maintained by Intel that describes a platform-independent method of interacting with the BMCs on servers. This advisory followed the release of numerous vulnerabilities in the IPMI 1.5 and 2.0 standards discovered by independent security consultant Dan Farmer while working on a DARPA grant.
Effectively, the vulnerabilities Farmer discovered allow unfettered access to the most basic functions of any server with an exposed and unpatched IPMI interface. Given that more than 200 server manufacturers have adopted Intel's standard (Hewlett-Packard, Dell, SuperMicro, IBM, you name it) and implemented it in their own BMCs, chances are your data center is full of enabled and accessible IPMI devices. Effectively, a hacker with full access to an IPMI interface might as well be physically sitting in front of the server -- that's the point of these interfaces.
Although Farmer's research centers on the widely used IPMI standard, the idea that a shadow set of black-box servers -- many using other protocols -- operate on our networks and run old, infrequently patched code over which we have very little control is extremely disturbing. You don't have to think very hard to come up with more devices just like this: printers, UPSes, power distribution hardware, network-attached storage appliances, time clocks, search appliances, you name it. We all run a lot of "invisible" servers on our networks -- sometimes without realizing it.