Simple Machines Forum (SMF) 1.1RCx before 1.1RC3, and 1.0.x before 1.0.8, does not properly unset variables when the input data includes a numeric parameter with a value matching an alphanumeric parameter's hash value, which allows remote attackers to perform directory traversal attacks to read arbitrary local files, lock topics, and possibly have other security impacts.  NOTE: it could be argued that this vulnerability is due to a bug in the unset PHP command (CVE-2006-3017) and the proper fix should be in PHP; if so, then this should not be treated as a vulnerability in Simple Machines Forum.