Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, the default configuration of client side sessions results in unencrypted, but signed, data being set as cookie values. This means that if something sensitive goes into the session, it could be read by something with access to the cookies. For this to be a vulnerability, some kind of sensitive data would need to be stored in the session and the session cookie would have to leak. For example, the cookies are not configured with httpOnly and an adjacent XSS vulnerability within the site allowed capture of the cookies. As of version 1.9.0, a securely randomly generated signing key is used. As a workaround, one may supply an encryption key, as per the documentation recommendation.