In the world of WordPress security, few topics are as misunderstood and poorly documented as WordPress authentication cookies and session management. While many online sources provide information about how WordPress manages sessions, the majority of them are outdated or inaccurate, often leading to confusion.

Basic Concepts

• Session: A session is used to store data across multiple HTTP requests. It often contains authentication information, preferences, and other arbitrary user data. A session is identified by a unique session ID, typically stored in a session cookie.
• Stateless Session: In a stateless session, the session data is stored on the client side (in the browser). Stateless sessions use methods like JSON Web Tokens (JWTs) to prevent tampering, and the server does not need to store session data.
• Authentication Cookie: WordPress uses authentication cookies to maintain a user’s logged-in state. These cookies contain data such as the session ID, user credentials, and expiration timestamp, and they are critical for the user’s access to a WordPress site without having to re-authenticate for each request.

How WordPress Manages Sessions?

Session Creation

When a user logs into WordPress, a session is initiated using the wp_set_auth_cookie function. This function performs several important tasks, including:

• Session Expiration: It sets the session expiration time, with a default of 2 days or 14 days if the user opts for “Remember Me”.
• Session ID Creation: It generates a unique session token (a random 43-character string) for the user.
• Signed Cookies: WordPress creates a pair of signed authentication cookies, which are sent to the user’s browser to maintain the session.

Authentication Cookies

WordPress creates two authentication cookies:

1. Auth Cookie: This is used to track the user’s login state across all pages.
2. Logged-in Cookie: This cookie is specifically for use in the admin area (/wp-admin), ensuring that only users who are logged in can access the backend.

Both cookies contain the session ID, and they are signed to prevent tampering. The cookies are also set with the httpOnly flag, meaning JavaScript cannot access them, thereby mitigating cross-site scripting (XSS) attacks.

Session Validation

When a user makes a subsequent request, WordPress validates their session by calling the wp_validate_auth_cookie function. This function checks the validity of the session using the data stored in the authentication cookies. If the session is valid, the user is granted access to the site.

A few key points about the validation process:

• It ensures the session has not been tampered with by verifying the cryptographic signature.
• It checks that the session ID exists in the user’s meta data, confirming that the session is legitimate.
• It supports the “log out elsewhere” functionality, which means users can invalidate their sessions across devices if they change their password.

Conclusion

WordPress has made significant improvements to its session management system, combining both server-side and stateless, signature-based sessions for enhanced security. While the system is generally robust against common threats such as XSS, session fixation, and brute-forcing, there are still areas for improvement.