Researchers for some time have demonstrated the possibility of one of virtualization's worst nightmares -- a guest virtual machine (VM) infiltrating and hacking its host system. Now another commercial tool is offering an exploit that does exactly that.

The newest version of Immunity's Canvas commercial penetration testing tool, v6.47, includes the so-called Cloudburst attack module, which was developed by Immunity researcher Kostya Kortchinsky to exploit a VMWare vulnerability (CVE-2009-1244) in VMware Workstation that lets a user or attacker in a "guest" VM break into the actual host operating environment. VMware issued a patch for the bug in April.

"Companies and administrators tend to trust that breaking out of a VM is not possible," says Nick Selby, director of the enterprise security practice at The 451 Group. "A lot of people consider this to be just another proof-of-concept. They don't understand that is a commercially available exploit."

Even though VMware has issued a patch, many enterprises may not necessarily have implemented it, Selby says. "We know that people don't patch," he adds.

Immunity's VM "breakout" exploit follows that of Core Security Technologies' VMware Shared Folders exploit in its Impact penetration testing tool announced last year. The module "weaponized" a vulnerability discovered by Core that lets an attacker create or alter executable files on the Windows host OS. For the attack to work, VMware's Shared Folders feature must be enabled and at least one folder on the underlying host system must be configured to share files with the VM.

Selby says Cloudburst is a more significant hack because it's a memory corruption-based method that lets an attacker access more of the system and do more damage. "This is memory corruption," he says. And Cloudburst works with default VM settings, such as having VM tools installed, he says.

The attack entails the guest VM executing malicious code on the host, and then tunnels a connection to it. VMWare Version 6.5.0 and 6.5.1 are affected, as well as all host operating systems, including Linux.

But there are simpler virtual machine "escape" methods than Cloudburst, notes HD Moore, creator of Metasploit and director of security architecture for BreakingPoint Systems. "There are some easy escape methods -- the host file system directory traversal -- that don't require exploit tools...you can abuse it from a standard shell," Moore says.

Moore says this type of attack is most worrisome for organizations that run disparate systems on the same VM host. That would mean "the cloud model where you are running systems for two unrelated customers on the same hardware, and you're concerned about an attack on one gaining access to the other," he says.

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