phpBB 2.0.21 does not properly handle pathnames ending in %00, which allows remote authenticated administrative users to upload arbitrary files, as demonstrated by a query to admin/admin_board.php with an avatar_path parameter ending in .php%00.
https://exchange.xforce.ibmcloud.com/vulnerabilities/28884
http://www.securityfocus.com/bid/21806
http://www.securityfocus.com/bid/20347
http://www.securityfocus.com/archive/1/445788/100/0/threaded
http://www.phpbb.com/phpBB/viewtopic.php?f=14&t=489624
http://www.debian.org/security/2008/dsa-1488
http://secunia.com/advisories/28871