ext/filter in PHP 5.2.0, when FILTER_SANITIZE_STRING is used with the FILTER_FLAG_STRIP_LOW flag, does not properly strip HTML tags, which allows remote attackers to conduct cross-site scripting (XSS) attacks via HTML with a '<' character followed by certain whitespace characters, which passes one filter but is collapsed into a valid tag, as demonstrated using %0b.
http://www.securityfocus.com/bid/22914
http://www.php-security.org/MOPB/MOPB-18-2007.html
http://www.novell.com/linux/security/advisories/2007_32_php.html
http://www.mandriva.com/security/advisories?name=MDKSA-2007:090
http://www.debian.org/security/2007/dsa-1283