Microsoft Internet Explorer 6 and 7 does not properly handle objects in memory, which allows remote attackers to execute arbitrary code by accessing a deleted object, aka "OnReadyStateChange Remote Code Execution Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A15573
https://exchange.xforce.ibmcloud.com/vulnerabilities/74381
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2012/ms12-023
http://www.us-cert.gov/cas/techalerts/TA12-101A.html