A critical vulnerability in VMware's virtualization software for Windows lets attackers escape the "guest" operating system and modify or add files to the underlying "host" operating system, the company has acknowledged. As of Sunday, there was no patch available for the flaw, which affects VMware's Windows client virtualization programs, including Workstation, Player, and ACE. The company's virtual machine software for Windows servers and for Mac- and Linux-based hosts are not at risk.
The bug was reported by Core Security Technologies, makers of the penetration-testing framework CORE IMPACT, said VMware in a security alert issued last Friday. "Exploitation of this vulnerability allows attackers to break out of an isolated guest system to compromise the underlying host system that controls it," claimed Core Security.
According to VMware, the bug is in the shared-folder feature of its Windows client-based virtualization software. Shared folders let users access certain files -- typically documents and other application-generated files -- from the host operating system and any virtual machine on that physical system.
"On Windows hosts, if you have configured a VMware host-to-guest shared folder, it is possible for a program running in the guest to gain access to the host's complete file system and create or modify executable files in sensitive locations," confirmed VMware.
VMware has not posted a fix, but it instead told users to disable shared folders.