Microsoft Internet Explorer 6 through 9, and 10 Consumer Preview, allows remote attackers to bypass Protected Mode or cause a denial of service (memory corruption) by leveraging access to a Low integrity process, as demonstrated by VUPEN during a Pwn2Own competition at CanSecWest 2012.
http://www.zdnet.com/blog/security/pwn2own-2012-ie-9-hacked-with-two-0day-vulnerabilities/10621
http://twitter.com/vupen/statuses/177895844828291073