VMware patches virtual machine escape issue on Windows

The code execution flaws affect the Windows versions of VMware Workstation, VMware Player and VMware Horizon Client. They were discovered by Kostya Kortchinsky of the Google Security Team and stem from a printer virtualization feature that allows a virtual machine's guest OS to access the printer attached to the host computer.

"On VMware Workstation 11.1, the virtual printer device is added by default to new VMs, and on recent Windows Hosts, the Microsoft XPS Document Writer is available as a default printer," Kortchinsky explained in an advisory. "Even if the VMware Tools are not installed in the Guest, the COM1 port can be used to talk to the Host printing Proxy."

An attacker with access to the guest OS can send EMFSPOOL and EMF files to the virtual COM1 serial port in order to exploit various vulnerabilities in the printer proxy process running on the host OS and then execute rogue code, the researcher said.

Some of the vulnerabilities can also be used to perform a denial-of-service attack against the Windows OS that runs the vulnerable VMware software.

VMware addressed the flaws in the newly released VMware Workstation 11.1.1 and 10.0.6; VMware Player 7.1.1 and 6.0.6 and the VMware Horizon Client for Windows 3.4.0, 3.2.1 and 5.4.2.

A workaround suggested by Kortchinsky is to "disconnect" the virtual printer from the guest OS or to remove it entirely from the virtual machine settings.

A separate input validation issue was identified for RPC commands in VMware Workstation 10.x, VMware Player 6.x, Fusion 7.x and 6.x, running on any supported platform. The flaw can be exploited to launch a denial-of-service attack against guest operating systems with the 32-bit architecture, or host operating systems with the 64-bit architecture.

To address this issue, users are advised to upgrade to VMware Workstation 10.0.5, VMware Player 6.0.6 or Fusion 7.0.1 and 6.0.6.