viewtopic.php in phpBB 2.0.12 and earlier allows remote attackers to obtain sensitive information via a highlight parameter containing invalid regular expression syntax, which reveals the path in a PHP error message.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2005-0604
http://www.phpbb.com/phpBB/viewtopic.php?t=267563
http://secunia.com/advisories/14413