Session fixation in Apache Wicket. org.apache.wicket.authroles.authentication.AuthenticatedWebSession is the authentication base class of Wicket's role-based security module, and its signIn(String, String) method is the entry point through which an application authenticates a session. Renewing the container session id at that point is the standard defence against an attacker who has fixed a session id in a victim's browser, and Wicket provides that renewal as org.apache.wicket.Session#changeSessionId(), whose documentation directs callers to invoke it on login for exactly that reason. AuthenticatedWebSession#signIn(String, String) calls it inside a guard that succeeds only on the first transition of the session's signed-in flag. The session id is therefore renewed when a session first signs in, and is not renewed when a session that is already signed in authenticates again. signIn(String, String) returns true either way, so neither the caller nor the application can tell that the renewal did not happen. An application is affected where it authenticates through AuthenticatedWebSession, which AuthenticatedWebApplication requires and which the shipped UsernamePasswordPanel uses, and where a session that is already signed in can authenticate again: a step-up prompt before a sensitive action, an account switch, or simply a sign-in form that stays reachable once the user is signed in. Nothing in the module hides that form from a signed-in session. Reaching the defect also requires an attacker to place a session id of their choosing in the victim's browser. JSESSIONID is set by the servlet container rather than by Wicket, so that needs a position Wicket does not grant, such as control of a host under the same registrable domain or a container configured to carry the session id in the URL, and the planted session has to be one the attacker has already signed in on, because a session that is not yet signed in does have its id renewed by the victim's authentication. An authentication attempt that fails signs the session out and closes the window. Applications that renew the session id in their own code after a successful authentication are not affected. As a workaround, renew the session id from the application's own code on every successful authentication, by calling Session#changeSessionId() at the end of the authenticate(String, String) implementation. This issue affects Apache Wicket: from 8.18.0 through 8.19.0, from 9.23.0 through 9.24.0, from 10.9.0 through 10.11.0. Users are recommended to upgrade to version 8.20.0, 9.25.0 or 10.12.0, which fix the issue.