The proof-of-concept rootkit, called SubVirt, exploits known security flaws and drops a VMM (virtual machine monitor) underneath a Windows or Linux installation.
Once the target operating system is hoisted into a virtual machine, the rootkit becomes impossible to detect because its state cannot be accessed by security software running in the target system, according to documentation seen by eWEEK.
The prototype, which will be presented at the IEEE Symposium on Security and Privacy later in 2006, is the brainchild of Microsofts Cybersecurity and Systems Management Research Group, the Redmond, Wash., unit responsible for the Strider GhostBuster anti-rootkit scanner and the Strider HoneyMonkey exploit detection patrol.
Today, anti-rootkit clean-up tools compare registry and file system API discrepancies to check for the presence of user-mode or kernel-mode rootkits, but this tactic is useless if the rootkit stores malware in a place that cannot be scanned.
"We used our proof-of concept [rootkits] to subvert Windows XP and Linux target systems and implemented four example malicious services," the researchers wrote in a technical paper describing the attack scenario.
"[We] assume the perspective of the attacker, who is trying to run malicious software and avoid detection. By assuming this perspective, we hope to help defenders understand and defend against the threat posed by a new class of rootkits," said the paper, which is co-written by researchers from the University of Michigan.
A virtual machine is one instance of an operating system running between the hardware and the "guest" operating system. Because the VM sits on the lower layer of the operating system, it is able to control the upper layers in a stealthy way.
"[T]he side that controls the lower layer in the system has a fundamental advantage in the arms race between attackers and defenders," the researchers said.
"If the defenders security service occupies a lower layer than the malware, then that security service should be able to detect, contain and remove the malware. Conversely, if the malware occupies a lower layer than the security service, then the malware should be able to evade the security service and manipulate its execution."
The group said the SubVirt project implemented VM-based rootkits on two platforms—Linux/VMWare and Windows/VirtualPC—and was able to write malicious services without detection.