pmwiki.php in PmWiki 2.1 beta 20, with register_globals enabled, allows remote attackers to bypass protection mechanisms that deregister global variables by setting both a GPC variable and a GLOBALS[] variable with the same name, which causes PmWiki to unset the GLOBALS[] variable but not the GPC variable, which creates resultant vulnerabilities such as remote file inclusion and cross-site scripting (XSS).