All Rack users, including all Padrino users, should upgrade their Rack dependency as soon as possible. Multiple severe issues have been found, one of them including a potential remote code execution. This is espcially important if you are using Rack::Session::Cookie, which Padrino activates by default. See the Rack website for details.
To upgrade, use:
bundle update rack
And make sure that you installed any of these versions: 1.5.2, 1.4.5, 1.3.10, 1.2.8, 1.1.6.