Cross-site scripting (XSS) vulnerability in the formatHTML function in includes/api/ApiFormatBase.php in MediaWiki before 1.19.12, 1.20.x and 1.21.x before 1.21.6, and 1.22.x before 1.22.3 allows remote attackers to inject arbitrary web script or HTML via a crafted string located after http:// in the text parameter to api.php.