Twig Sandbox Escape by authenticated users with access to editing CMS templates when safemode is enabled.

@@ -15,6 +15,7 @@
 use BackendAuth;
 use Twig\Environment as TwigEnvironment;
 use Twig\Cache\FilesystemCache as TwigCacheFilesystem;
+use Twig\Extension\SandboxExtension;
 use Cms\Twig\Loader as TwigLoader;
 use Cms\Twig\DebugExtension;
 use Cms\Twig\Extension as CmsTwigExtension;
@@ -23,6 +24,7 @@
 use System\Helpers\View as ViewHelper;
 use System\Classes\CombineAssets;
 use System\Twig\Extension as SystemTwigExtension;
+use System\Twig\SecurityPolicy;
 use October\Rain\Exception\AjaxException;
 use October\Rain\Exception\ValidationException;
 use October\Rain\Parse\Bracket as TextParser;
@@ -608,6 +610,7 @@ protected function initTwigEnvironment()
         $this->twig = new TwigEnvironment($this->loader, $options);
         $this->twig->addExtension(new CmsTwigExtension($this));
         $this->twig->addExtension(new SystemTwigExtension);
+        $this->twig->addExtension(new SandboxExtension(new SecurityPolicy, true));
 
         if ($isDebugMode) {
             $this->twig->addExtension(new DebugExtension($this));

@@ -19,6 +19,7 @@
 use System\Twig\Engine as TwigEngine;
 use System\Twig\Loader as TwigLoader;
 use System\Twig\Extension as TwigExtension;
+use System\Twig\SecurityPolicy as TwigSecurityPolicy;
 use System\Models\EventLog;
 use System\Models\MailSetting;
 use System\Classes\CombineAssets;
@@ -27,6 +28,7 @@
 use October\Rain\Router\Helper as RouterHelper;
 use Illuminate\Pagination\Paginator;
 use Illuminate\Support\Facades\Schema;
+use Twig\Extension\SandboxExtension;
 
 class ServiceProvider extends ModuleServiceProvider
 {
@@ -297,6 +299,7 @@ protected function registerTwigParser()
         App::singleton('twig.environment', function ($app) {
             $twig = new TwigEnvironment(new TwigLoader, ['auto_reload' => true]);
             $twig->addExtension(new TwigExtension);
+            $twig->addExtension(new SandboxExtension(new TwigSecurityPolicy, true));
             return $twig;
         });
 

@@ -0,0 +1,61 @@
+<?php namespace System\Twig;
+
+use Twig\Markup;
+use Twig\Template;
+use Twig\Sandbox\SecurityPolicyInterface;
+use Twig\Sandbox\SecurityNotAllowedMethodError;
+use Twig\Sandbox\SecurityNotAllowedPropertyError;
+
+/**
+ * SecurityPolicy globally blocks accessibility of certain methods and properties.
+ *
+ * @package october\system
+ * @author Alexey Bobkov, Samuel Georges
+ */
+final class SecurityPolicy implements SecurityPolicyInterface
+{
+    protected $blockedProperties = [];
+
+    protected $blockedMethods = [
+        'addDynamicMethod',
+        'addDynamicProperty'
+    ];
+
+    public function __construct()
+    {
+        $this->setBlockedMethods($this->blockedMethods);
+    }
+
+    public function setBlockedMethods(array $methods)
+    {
+        foreach ($this->blockedMethods as $i => $m) {
+            $this->blockedMethods[$i] = strtr($m, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz');
+        }
+    }
+
+    public function checkSecurity($tags, $filters, $functions)
+    {
+    }
+
+    public function checkMethodAllowed($obj, $method)
+    {
+        if ($obj instanceof Template || $obj instanceof Markup) {
+            return;
+        }
+
+        $blockedMethod = strtr($method, 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz');
+
+        if (in_array($blockedMethod, $this->blockedMethods)) {
+            $class = get_class($obj);
+            throw new SecurityNotAllowedMethodError(sprintf('Calling "%s" method on a "%s" object is blocked.', $method, $class), $class, $method);
+        }
+    }
+
+    public function checkPropertyAllowed($obj, $property)
+    {
+        if (in_array($property, $this->blockedProperties)) {
+            $class = get_class($obj);
+            throw new SecurityNotAllowedPropertyError(sprintf('Calling "%s" property on a "%s" object is blocked.', $property, $class), $class, $property);
+        }
+    }
+}