GHSA-9j94-67jr-4cqj Rack session gets restored after deletion

• RubyGems rack-session: >= 2.0.0, < 2.1.1 → fixed in 2.1.1

Summary When using the `Rack::Session::Pool` middleware, simultaneous rack requests can restore a deleted rack session, which allows the unauthenticated user to occupy that session. Details Rack session middleware prepares the session at the beginning of request, then saves is back to the store with possible changes applied by host rack application. This way the session becomes to be a subject of race conditions in general sense over concurrent rack requests. Impact 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. Mitigation • Update to the latest version of `rack-session`, or • Ensure your application invalidates sessions atomically by marking them as logged out e.g., using a `logged_out` flag, instead of deleting them, and check this flag on every request to prevent reuse, or • Implement a custom session store that tracks session invalidation timestamps and refuses to accept session data if the session was invalidated after the request began. Related This code was previously part of `rack` in Rack for the equivalent advisory in `rack` (affecting Rack < 3 only).