Multiple cross-site scripting (XSS) vulnerabilities in TWiki before 5.1.0 allow remote attackers to inject arbitrary web script or HTML via (1) the newtopic parameter in a WebCreateNewTopic action, related to the TWiki.WebCreateNewTopicTemplate topic; or (2) the query string to SlideShow.pm in the SlideShowPlugin.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.