Concorde, formerly know as Nexkey, is a fork of the federated microblogging platform Misskey. Prior to version 12.25Q1.1, due to an improper implementation of the logout process, authentication credentials remain in cookies even after a user has explicitly logged out, which may allow an attacker to steal authentication tokens. This could have devastating consequences if a user with admin privileges is (or was) using a shared device. Users who have logged in on a shared device should go to Settings > Security and regenerate their login tokens. Version 12.25Q1.1 fixes the issue. As a workaround, clear cookies and site data in the browser after logging out.
According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."