The wfMangleFlashPolicy function in OutputHandler.php in MediaWiki before 1.19.22, 1.20.x through 1.22.x before 1.22.14, and 1.23.x before 1.23.7 allows remote attackers to conduct PHP object injection attacks via a crafted string containing <cross-domain-policy> in a PHP format request, which causes the string length to change when converting the request to <NOT-cross-domain-policy>.