VMware has released Fusion 2.0.4 to plug the hole.

According to Kostya Kortchinsky, an exploit researcher at Immunity Inc., a critical vulnerability in VMware's virtual machine display function can be used to read and write memory on the "host" operating system -- the OS running the physical hardware.

Kortchinsky crafted an exploit for Immunity's customers -- the Miami-based company is best-known for its Canvas penetration testing tool -- and posted a that demonstrates an attack on a machine running Windows Vista Service Pack 1 (SP1) as the host operating system, and Windows XP as the "guest," the OS running in a virtual machine.

"This is indeed a guest-to-host exploit," Kortchinsky said in an e-mail today. "It uses several vulnerabilities in the 'Display functions' (as VMware put it) that allow [someone] to read and write arbitrary memory in the host. Thus the guest can run some code on the host, effectively bypassing ASLR and DEP on Vista SP1."

The same tactics can be employed against a guest operating system -- say Windows XP -- running in Fusion on a Mac powered by Apple's Mac OS X, Kortchinsky confirmed. "The vulnerability is also present in VMware Fusion and as such would allow a guest (Windows or Linux) to run code on the Mac OS X host," he said. "We didn't implement this exploit though, but will probably in a near future."