# Twig Sandbox

The `sandbox` extension can be used to evaluate untrusted code.

## Registering the Sandbox

Register the `SandboxExtension` extension via the `addExtension()` method:

    $twig->addExtension(new \Twig\Extension\SandboxExtension($policy));

## Configuring the Sandbox Policy

The sandbox security is managed by a policy instance, which must be passed to the `SandboxExtension` constructor.

By default, Twig comes with one policy class: `\Twig\Sandbox\SecurityPolicy`. This class allows you to allow-list some tags, filters, functions, but also properties and methods on objects:

    $tags = ['if'];
    $filters = ['upper'];
    $methods = [
        'Article' => ['getTitle', 'getBody'],
    ];
    $properties = [
        'Article' => ['title', 'body'],
    ];
    $functions = ['range'];
    $policy = new \Twig\Sandbox\SecurityPolicy($tags, $filters, $methods, $properties, $functions);

With the previous configuration, the security policy will only allow usage of the `if` tag, and the `upper` filter. Moreover, the templates will only be able to call the `getTitle()` and `getBody()` methods on `Article` objects, and the `title` and `body` public properties. Everything else won’t be allowed and will generate a `\Twig\Sandbox\SecurityError` exception.

Note

As of Twig 3.14.1 (and on Twig 3.11.2), if the `Article` class implements the `ArrayAccess` interface, the templates will only be able to access the `title` and `body` attributes.

Note that native array-like classes (like `ArrayObject`) are always allowed, you don’t need to configure them.

Caution

The `extends` and `use` tags are always allowed in a sandboxed template. That behavior will change in 4.0 where these tags will need to be explicitly allowed like any other tag.

## Enabling the Sandbox

By default, the sandbox mode is disabled and should be enabled when including untrusted template code by using the `sandboxed` option of the `include` function:

    {{ include('user.html.twig', sandboxed: true) }}

You can sandbox all templates by passing `true` as the second argument of the extension constructor:

    $sandbox = new \Twig\Extension\SandboxExtension($policy, true);

## Accepting Callables Arguments

The Twig sandbox allows you to configure which functions, filters, tests and dot operations are allowed. Many of these calls can accept arguments. As these arguments are not validated by the sandbox, you must be very careful.

For instance, accepting a PHP `callable` as an argument is dangerous as it allows end user to call any PHP function (by passing a `string`) or any static methods (by passing an `array`). For instance, it would accept any PHP built-in functions like `system()` or `exec()`:

    $twig->addFilter(new \Twig\TwigFilter('custom', function (callable $callable) {
        // ...
        $callable();
        // ...
    }));

To avoid this security issue, don’t type-hint such arguments with `callable` but use `\Closure` instead (not using a type-hint would also be problematic). This restricts the allowed callables to PHP closures only, which is enough to accept Twig arrow functions:

    $twig->addFilter(new \Twig\TwigFilter('custom', function (\Closure $callable) {
        // ...
        $callable();
        // ...
    }));

    {{ people|custom(p => p.username|join(', ') }}

Any PHP callable can easily be converted to a closure by using the first-class callable syntax.