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.