Microsoft Internet Explorer 5 SP4 and 6 do not properly garbage collect when "multiple imports are used on a styleSheets collection" to construct a chain of Cascading Style Sheets (CSS), which allows remote attackers to execute arbitrary code via unspecified vectors.
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A5
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2006/ms06-042
http://www.zerodayinitiative.com/advisories/ZDI-06-026.html
http://www.vupen.com/english/advisories/2006/3212
http://www.us-cert.gov/cas/techalerts/TA06-220A.html
http://www.securityfocus.com/bid/19316
http://www.securityfocus.com/archive/1/442578/100/0/threaded
http://www.kb.cert.org/vuls/id/262004
http://securitytracker.com/id?1016663