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).
https://exchange.xforce.ibmcloud.com/vulnerabilities/24368
https://exchange.xforce.ibmcloud.com/vulnerabilities/24367
https://exchange.xforce.ibmcloud.com/vulnerabilities/24366
http://www.vupen.com/english/advisories/2006/0375
http://www.ush.it/2006/01/24/pmwiki-multiple-vulnerabilities/
http://www.securityfocus.com/bid/16421
http://securitytracker.com/id?1015550
http://secunia.com/advisories/18634
http://archives.neohapsis.com/archives/fulldisclosure/2006-01/0931.html