Microsoft Internet Explorer 6 through 9, and 10 Consumer Preview, does not properly handle objects in memory, which allows remote attackers to execute arbitrary code by attempting to access a nonexistent object, leading to a heap-based buffer overflow, aka "Col Element Remote Code Execution Vulnerability," as demonstrated by VUPEN during a Pwn2Own competition at CanSecWest 2012.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A15539
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2012/ms12-037
http://www.zdnet.com/blog/security/pwn2own-2012-ie-9-hacked-with-two-0day-vulnerabilities/10621
http://www.us-cert.gov/cas/techalerts/TA12-164A.html
http://twitter.com/vupen/statuses/177895844828291073