CVE-2026-39324 Rack::Session::Cookie secrets: decrypt failure fallback enables secretless session forgery and Marshal deserialization

Rack::Session is a session management implementation for Rack. From 2.0.0 to before 2.1.2, Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie...