What is the potential issue with using session variables in PHP when including one PHP file in another?

When including one PHP file in another, session variables may not be accessible if the session has not been started in both files. To solve this issue, you can ensure that the session is started in each PHP file by calling session_start() at the beginning of each file. 

<?php
// File 1: session_start.php
session_start();
$_SESSION['username'] = 'John';

// File 2: include_file.php
session_start();
echo $_SESSION['username'];
?>

Keywords

session variables PHP file inclusion variable scope data integrity security vulnerability

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