CVE-2015-3226: XSS Vulnerability in ActiveSupport::JSON.encode

When a Hash containing user-controlled data is encoded as JSON (either through Hash#to_json or ActiveSupport::JSON.encode), Rails does not perform adequate escaping that matches the guarantee implied by the escape_html_entities_in_json option (which is enabled by default). If this resulting JSON string is subsequently inserted directly into an HTML page, the page will be vulnerable to XSS attacks.