Anti-CSRF Library

Motivation

There aren't any good session-powered CSRF prevention libraries. By good we mean:

• CSRF tokens can be restricted to any or all of the following:
  • A particular session
  • A particular HTTP URI
  • A particular IP address (optional)
• Multiple CSRF tokens can be stored
• CSRF tokens expire after one use
• An upper limit on the number of tokens stored with session data is enforced
  • In our implementation, the oldest are removed first

Warning - Do not use in any project where all $_SESSION data is stored client-side in a cookie. This will quickly run up the 4KB storage max for an HTTP cookie.

Using it in Any Project

See autoload.php for an SPL autoloader.

Using it with Twig templates

First, add a filter like this one:

use \ParagonIE\AntiCSRF\AntiCSRF;
$twigEnv->addFunction(
    new \Twig_SimpleFunction(
        'form_token',
        function($lock_to = null) {
            static $csrf;
            if ($csrf === null) {
                $csrf = new AntiCSRF;
            }
            return $csrf->insertToken($lock_to, false);
        },
        ['is_safe' => ['html']]
    )
);

Next, call the newly created form_token function from your templates.

<form action="/addUser.php" method="post">
    {{ form_token("/addUser.php") }}

    {# ... the rest of your form here ... #}
</form>

Validating a Request

    $csrf = new \ParagonIE\AntiCSRF\AntiCSRF;
    if (!empty($_POST)) {
        if ($csrf->validateRequest()) {
            // Valid
        } else {
            // Log a CSRF attack attempt
        }
    }