Rack session gets restored after deletion

Rack::Session is a session management implementation for Rack. In versions starting from 2.0.0 to before 2.1.1, when using the Rack::Session::Pool middleware, and provided the attacker can acquire a session cookie (already a major issue), the session may be restored if the attacker can trigger a long running request (within that same session) adjacent to the user logging out, in order to retain illicit access even after a user has attempted to logout. This issue has been patched in version 2.1.1.