The bbencode_second_pass and make_clickable functions in bbcode.php for phpBB before 2.0.15, as used in viewtopic.php, privmsg.php, and other scripts, allow remote attackers to execute arbitrary script via a BBcode tag with a (1) javascript:, (2) applet:, (3) about:, (4) activex:, (5) chrome:, or (6) script: URI scheme, as demonstrated using the URL tag.
https://exchange.xforce.ibmcloud.com/vulnerabilities/20574
http://www.securityfocus.com/bid/13545
http://www.phpbb.com/phpBB/viewtopic.php?f=14&t=288194
http://www.kb.cert.org/vuls/id/113196
http://securitytracker.com/id?1014117
http://securitytracker.com/id?1013918
http://secunia.com/advisories/15298
http://seclists.org/lists/bugtraq/2005/May/0098.html