VMware Workstation before 5.5.4, when running a 64-bit Windows guest on a 64-bit host, allows local users to "corrupt the virtual machine's register context" by debugging a local program and stepping into a "syscall instruction."
https://exchange.xforce.ibmcloud.com/vulnerabilities/33993
http://www.vupen.com/english/advisories/2007/1592
http://www.vmware.com/support/ws55/doc/releasenotes_ws55.html#554
http://www.securitytracker.com/id?1018011
http://www.securityfocus.com/bid/23732
http://www.securityfocus.com/archive/1/469011/30/6510/threaded
http://www.securityfocus.com/archive/1/467936/30/6690/threaded