Contao is an open source content management system. Prior to version 4.13.40, when a frontend member changes their password in the personal data or the password lost module, the corresponding remember-me tokens are not removed. If someone compromises an account and is able to get a remember-me token, changing the password would not be enough to reclaim control over the account. Version 4.13.40 contains a fix for the issue. As a workaround, disable "Allow auto login" in the login module.
Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.
According to WASC, "Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization."