James, a hacker, identifies a vulnerability in a website.

James, a hacker, identifies a vulnerability in a website. To exploit the vulnerability, he visits the login page and notes down the session ID that is created. He appends this session ID to the login URL and shares the link with a victim. Once the victim logs into the website using the shared URL, James reloads the webpage (containing the URL with the session ID appended) and now, he can browse the active session of the victim. Which attack did James successfully execute?