The PerfectNav plugin for Microsoft Internet Explorer allows remote attackers to cause a denial of service (browser crash) via a malformed URL such as "?".
https://exchange.xforce.ibmcloud.com/vulnerabilities/15326
http://www.securityfocus.com/bid/9753
http://securitytracker.com/id?1009218
http://securetarget.net/advisory.htm
http://lists.grok.org.uk/pipermail/full-disclosure/2004-February/017830.html