What is CSRF?

CSRF, or Cross-Site Request Forgery, is a type of attack where a malicious site tricks a user into submitting a request that they did not intend. This can result in unauthorized actions such as changing account information or transferring funds.

How Does CSRF Work?

CSRF attacks exploit authenticated sessions. Here’s how it works:

1. A user logs into a trusted web application.
2. The user visits a malicious website while still logged in.
3. The malicious site sends a forged request to the trusted application using the user’s credentials.

Best Practices to Prevent CSRF

• Use CSRF Tokens: Add unique tokens to every sensitive form submission.
• Validate HTTP Referer Headers: Check if the request originates from a trusted source.
• Enable SameSite Cookies: Restrict cookies to same-site requests only.
• Implement CAPTCHA: Add an extra layer of human verification to prevent automated attacks.

Implementing CSRF Tokens in PHP

Here’s an example of how to implement CSRF tokens in PHP:

<?php
session_start();
if (empty($_SESSION['csrf_token'])) {
    $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
}
?>
<form action="process.php" method="POST">
    <input type="hidden" name="csrf_token" value="<?php echo $_SESSION['csrf_token']; ?>">
    <button type="submit">Submit</button>
</form>
            

And validate the token on the server:

<?php
session_start();
if ($_POST['csrf_token'] !== $_SESSION['csrf_token']) {
    die("Invalid CSRF token.");
}
?>

Conclusion

Preventing CSRF attacks is crucial to protecting your users and application. By implementing CSRF tokens, validating requests, and following the best practices above, you can significantly reduce the risk of such attacks.