phpBB 1.4.4 and earlier with BBcode allows remote attackers to cause a denial of service (CPU consumption) and corrupt the database via null \0 characters within [code] tags.
phpBB 2.0.20 does not verify user-specified input variable types before being passed to type-dependent functions, which allows remote attackers to obtain sensitive information, as demonstrated by the (1) mode parameter to memberlist.php and the (2) highlight parameter to viewtopic.php that are used as an argument to the htmlspecialchars or urlencode functions, which displays the installation path in the resulting error message.