Microsoft Internet Explorer 6.0 on Windows NT 4.0 SP6a, Windows 2000 SP4, Windows XP SP1, Windows XP SP2, and Windows Server 2003 SP1 allows remote attackers to cause a denial of service (client crash) via a certain combination of a malformed HTML file and a CSS file that triggers a null dereference, probably related to rendering of a DIV element that contains a malformed IMG tag, as demonstrated by IEcrash.htm and IEcrash.rar.