What potential issue can arise when using $_SESSION in PHP?

One potential issue that can arise when using $_SESSION in PHP is the possibility of session fixation attacks. This occurs when an attacker sets a user's session ID before the user logs in, allowing the attacker to hijack the session. To prevent this, you can regenerate the session ID whenever a user authenticates, effectively invalidating any previously set session IDs.

session_start();

// Check if the user is authenticated
if ($authenticated) {
    // Regenerate session ID
    session_regenerate_id(true);
}