Backend routing

Each request to the backend is eventually executed by a controller. A list of routes is defined which maps a given request to a controller and an action.

Routes are defined inside extensions, in the files

  • Configuration/Backend/Routes.php for general requests
  • Configuration/Backend/AjaxRoutes.php for Ajax calls

Here is an extract of EXT:backend/Configuration/Backend/Routes.php (GitHub):

EXT:backend/Configuration/Backend/Routes.php (excerpt) 
<?php

use TYPO3\CMS\Backend\Controller;

return [
    // Login screen of the TYPO3 Backend
    'login' => [
        'path' => '/login',
        'access' => 'public',
        'target' => Controller\LoginController::class . '::formAction'
    ],

    // Main backend rendering setup (previously called backend.php) for the TYPO3 Backend
    'main' => [
        'path' => '/main',
        'referrer' => 'required,refresh-always',
        'target' => Controller\BackendController::class . '::mainAction'
    ],
    // ...
];
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So, a route file essentially returns an array containing route mappings. A route is defined by a key, a path, a referrer and a target. The "public" access property indicates that no authentication is required for that action.

Backend routing and cross-site scripting

Public backend routes (those having option 'access' => 'public') do not require any session token, but can be used to redirect to a route that requires a session token internally. For this context, the backend user logged in must have a valid session.

This scenario can lead to situations where an existing cross-site scripting vulnerability (XSS) bypasses the mentioned session token, which can be considered cross-site request forgery (CSRF). The difference in terminology is that this scenario occurs on same-site requests and not cross-site - however, potential security implications are still the same.

Backend routes can enforce the existence of an HTTP referrer header by adding a referrer to routes to mitigate the described scenario.

'main' => [
    'path' => '/main',
    'referrer' => 'required,refresh-empty',
    'target' => Controller\BackendController::class . '::mainAction'
],
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Values for referrer are declared as a comma-separated list:

  • required enforces existence of HTTP Referer header that has to match the currently used backend URL (for example, https://example.org/typo3/), the request will be denied otherwise.
  • refresh-empty triggers an HTML-based refresh in case HTTP Referer header is not given or empty - this attempt uses an HTML refresh, since regular HTTP Location redirect still would not set a referrer. It implies this technique should only be used on plain HTML responses and will not have any impact, for example, on JSON or XML response types.

This technique should be used on all public routes (without session token) that internally redirect to a restricted route (having a session token). The goal is to protect and keep information about the current session token internal.

The request sequence in the TYPO3 Core looks like this:

  1. HTTP request to https://example.org/typo3/ having a valid user session
  2. Internally public backend route /login is processed
  3. Internally redirects to restricted backend route /main since an existing and valid backend user session was found + HTTP redirect to https://example.org/typo3/main?token=... + exposing the token is mitigated with referrer route option mentioned above

Generating backend URLs

Using the UriBuilder API, you can generate any kind of URL for the backend, may it be a module, a typical route or an Ajax call. Therefore use either buildUriFromRoute() or buildUriFromRoutePath(). The UriBuilder then returns a PSR-7 conform Uri object that can be cast to a string when needed. Furthermore, the UriBuilder automatically generates and applies the mentioned session token.

Example within a controller (we use here a non-Extbase controller):

EXT:my_extension/Classes/Controller/MyRouteController.php 
<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\Controller;

use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use TYPO3\CMS\Backend\Routing\UriBuilder;

final class MyRouteController
{
    private UriBuilder $uriBuilder;

    public function __construct(UriBuilder $uriBuilder)
    {
        $this->uriBuilder = $uriBuilder;
    }

    public function handle(ServerRequestInterface $request): ResponseInterface
    {
        // .. do some stuff

        // Using a route identifier
        $uri = $this->uriBuilder->buildUriFromRoute(
            'web_layout',
            ['id' => 42]
        );

        // Using a route path
        $uri = $this->uriBuilder->buildUriFromRoutePath(
            '/record/edit',
            [
                'edit' => [
                    'pages' => [
                        123 => 'edit',
                    ],
                ],
            ]
        );

        // ... do some other stuff
    }
}
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More Information

Please refer to the following resources and look at how the TYPO3 source code handles backend routing in your TYPO3 version.