source: http://www.securityfocus.com/bid/10724/info

It is reported that it is possible to bypass PHPs strip_tags() function.

It is reported that under certain circumstances, PHPs strip_tags() function will improperly leave malformed tags in place.

This vulnerability may mean that previously presumed-safe web applications could contain multiple cross-site scripting and HTML injection vulnerabilities when viewed by Microsoft Internet Explorer or Apple Safari web browsers.

It is reported that 'magic_quotes_gpc' must be off for PHP to be vulnerable to this issue. 

If a web application uses strip_tags() similar to:
$example = strip_tags($_REQUEST['user_input'], "<b><i><s>");

Then possible tags that may lead to exploitation might be:
<\0script> or <s\0cript>