I really can't understand the session fixation attack.
I've read OWASP definition that said:
Session Fixation is an attack that permits an attacker to hijack a valid user session. The attack explores a limitation in the way the web application manages the session ID, more specifically the vulnerable web application. When authenticating a user, it doesn’t assign a new session ID, making it possible to use an existent session ID. The attack consists of obtaining a valid session ID (e.g. by connecting to the application), inducing a user to authenticate himself with that session ID, and then hijacking the user-validated session by the knowledge of the used session ID. The attacker has to provide a legitimate Web application session ID and try to make the victim's browser use it.
At the same time, I read this report, and the security researcher says that this vulnerability is session fixation session fixation report:
The application does not set a new Session ID in the cookie after what appears to be an authentication attempt by the user. If this was a successful login and the Session IDs are stored in cookies then this application is affected by Session Fixation vulnerability.
My question is: is the vulnerability in this report session fixation, and is the steps of testing this vulnerability the steps of testing session fixation?