There is a potential DOM based cross-site scripting issue in rails-ujs which leverages the Clipboard API to target HTML elements that are assigned the contenteditable attribute. This has the potential to occur when pasting malicious HTML content from the clipboard that includes a data-method, data-remote or data-disable-with attribute.

jquery_ujs.js in jquery-rails before 3.1.3 and 4.x before 4.0.4 and rails.js in jquery-ujs before 1.0.4, as used with Ruby on Rails 3.x and 4.x, allow remote attackers to bypass the Same Origin Policy, and trigger transmission of a CSRF token to a different-domain web server, via a leading space character in a URL within an attribute value.