Unsure if there are any currently publicly known exploits, but it sure isn't unheard of for VirtualBox:
* http://arstechnica.com/security/2015/05/extremely-serious-vi...
* http://www.securityfocus.com/archive/1/495095
* https://www.cert.be/advisories/oracle-vm-virtualbox-two-priv...
* http://www.coresecurity.com/content/virtualbox-privilege-esc...