phpBB 2.0.17 and earlier, when the register_long_arrays directive is disabled, allows remote attackers to modify global variables and bypass security mechanisms because PHP does not define the associated HTTP_* variables.
http://www.securityfocus.com/bid/15243
http://www.hardened-php.net/advisory_172005.75.html
http://www.debian.org/security/2005/dsa-925
http://securitytracker.com/id?1015121
http://securityreason.com/securityalert/130
http://secunia.com/advisories/18098