Session fixation is a kind of attack to rope victims in using specified session ID. Attacking processes are: 1. attackers reset the session ID of target user and listen to session state; 2. the target user logins the site using specified session ID; 3. attackers will obtain the legal session. This rule supports to defend the A7: Identification and Authentication Failures of OWASP Top 10 - 2021. Other reference:None