Microsoft Internet Explorer 6 and 7 for Windows XP SP2 and SP3; 6 and 7 for Server 2003 SP2; 7 for Vista Gold, SP1, and SP2; and 7 for Server 2008 SP2 does not properly synchronize AJAX requests, which allows allows remote attackers to execute arbitrary code via a large number of concurrent, asynchronous XMLHttpRequest calls, aka "HTML Object Memory Corruption Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A6260
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2009/ms09-019
http://www.zerodayinitiative.com/advisories/ZDI-09-037
http://www.vupen.com/english/advisories/2009/1538
http://www.us-cert.gov/cas/techalerts/TA09-160A.html
http://www.securitytracker.com/id?1022350
http://www.securityfocus.com/bid/35222
http://www.securityfocus.com/archive/1/504206/100/0/threaded