diff --git a/CHANGELOG.md b/CHANGELOG.md
index bf8801ba689..903179f37dc 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Most classes can now be instantiated via the `create()` Twig function. ([#18376](https://github.com/craftcms/cms/discussions/18376))
 - Fixed a bug where element search query caches weren’t getting invalidated when elements’ search keywords were indexed. ([#18275](https://github.com/craftcms/cms/issues/18275))
 
 ## 4.17.12 - 2026-03-26
diff --git a/src/filters/SecFetchSiteFilter.php b/src/filters/SecFetchSiteFilter.php
new file mode 100644
index 00000000000..fde065fde27
--- /dev/null
+++ b/src/filters/SecFetchSiteFilter.php
@@ -0,0 +1,74 @@
+<?php
+/**
+ * @link https://craftcms.com/
+ * @copyright Copyright (c) Pixel & Tonic, Inc.
+ * @license https://craftcms.github.io/license/
+ */
+
+namespace craft\filters;
+
+use Craft;
+use yii\base\ActionFilter;
+use yii\web\BadRequestHttpException;
+
+/**
+ * Action filter for validating the `Sec-Fetch-Site` header.
+ *
+ * @since 4.18.0
+ */
+class SecFetchSiteFilter extends ActionFilter
+{
+    use ConditionalFilterTrait;
+
+    /**
+     * Whether to use origin verification only (no CSRF token fallback).
+     */
+    public bool $originOnly = true;
+
+    /**
+     * Whether to accept `same-site` in addition to `same-origin` (e.g. subdomains).
+     */
+    public bool $allowSameSite = false;
+
+    public string $headerName = 'Sec-Fetch-Site';
+
+    public ?string $errorMessage = null;
+
+    public ?array $safeMethods = null;
+
+    /**
+     * @inheritdoc
+     */
+    public function beforeAction($action): bool
+    {
+        $this->setDefaults();
+
+        $request = Craft::$app->getRequest();
+
+        if (in_array($request->getMethod(), $this->safeMethods, true)) {
+            return true;
+        }
+
+        $secFetchSite = $request->getHeaders()->get($this->headerName);
+
+        if ($secFetchSite === 'same-origin') {
+            return true;
+        }
+
+        if ($secFetchSite === 'same-site' && $this->allowSameSite) {
+            return true;
+        }
+
+        if ($this->originOnly) {
+            throw new BadRequestHttpException($this->errorMessage);
+        }
+
+        return true;
+    }
+
+    private function setDefaults(): void
+    {
+        $this->safeMethods = $this->safeMethods ?? Craft::$app->getRequest()->csrfTokenSafeMethods;
+        $this->errorMessage = $this->errorMessage ?? Craft::t('yii', 'Unable to verify your data submission.');
+    }
+}
diff --git a/src/web/twig/Extension.php b/src/web/twig/Extension.php
index 40140479513..d727bd69cb7 100644
--- a/src/web/twig/Extension.php
+++ b/src/web/twig/Extension.php
@@ -64,9 +64,13 @@
 use DateTime;
 use DateTimeInterface;
 use DateTimeZone;
+use DirectoryIterator;
+use GuzzleHttp\Psr7\FnStream;
 use Illuminate\Support\Collection;
 use IteratorAggregate;
 use Money\Money;
+use SimpleXMLElement;
+use Symfony\Component\Process\Process;
 use Throwable;
 use Traversable;
 use Twig\DeprecatedCallableInfo;
@@ -82,6 +86,7 @@
 use yii\base\BaseObject;
 use yii\base\InvalidArgumentException;
 use yii\base\InvalidConfigException;
+use yii\behaviors\AttributeTypecastBehavior;
 use yii\db\Exception;
 use yii\db\Expression;
 use yii\db\QueryInterface;
@@ -1495,11 +1500,22 @@ public function collectFunction(mixed $var): Collection
     public function createFunction(string|array $type, array $params = []): object
     {
         $class = is_string($type) ? $type : ($type['__class'] ?? $type['class'] ?? null);
-        if (
-            !is_subclass_of($class, BaseObject::class) &&
-            !str_starts_with($class, 'craft\\helpers\\')
-        ) {
-            throw new InvalidArgumentException(sprintf('create() can only be used to create instances of %s.', BaseObject::class));
+        if (!$class) {
+            throw new InvalidArgumentException('No class specified for create().');
+        }
+
+        $blocklist = [
+            AttributeTypecastBehavior::class,
+            DirectoryIterator::class,
+            FnStream::class,
+            Process::class,
+            SimpleXMLElement::class,
+        ];
+
+        foreach ($blocklist as $c) {
+            if (is_a($class, $c, true)) {
+                throw new InvalidArgumentException(sprintf('create() cannot be used to create instances of %s.', $class));
+            }
         }
 
         /** @var BaseObject */
diff --git a/tests/unit/filters/SecFetchSiteFilterTest.php b/tests/unit/filters/SecFetchSiteFilterTest.php
new file mode 100644
index 00000000000..5b9e2a83060
--- /dev/null
+++ b/tests/unit/filters/SecFetchSiteFilterTest.php
@@ -0,0 +1,111 @@
+<?php
+/**
+ * @link https://craftcms.com/
+ * @copyright Copyright (c) Pixel & Tonic, Inc.
+ * @license https://craftcms.github.io/license/
+ */
+
+namespace crafttests\unit\filters;
+
+use Craft;
+use craft\filters\SecFetchSiteFilter;
+use craft\test\TestCase;
+use craft\web\Request;
+use yii\base\Action;
+use yii\web\BadRequestHttpException;
+use yii\web\Controller;
+
+/**
+ * Unit tests for SecFetchSiteFilter
+ *
+ * @author Pixel & Tonic, Inc. <support@pixelandtonic.com>
+ * @since 4.18.0
+ */
+class SecFetchSiteFilterTest extends TestCase
+{
+    private SecFetchSiteFilter $filter;
+    private Action $action;
+    private Request $request;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $controller = $this->createMock(Controller::class);
+        $this->action = new Action('test-action', $controller);
+        $this->filter = new SecFetchSiteFilter();
+        $this->request = Craft::$app->getRequest();
+    }
+
+    public function testAllowsSameOriginForUnsafeMethods(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'same-origin');
+
+        self::assertTrue($this->filter->beforeAction($this->action));
+    }
+
+    public function testAllowsSameSiteWhenConfigured(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'same-site');
+
+        $this->filter->allowSameSite = true;
+        self::assertTrue($this->filter->beforeAction($this->action));
+    }
+
+    public function testAllowsFallbackWhenHeaderMissingAndNotOriginOnly(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->remove('Sec-Fetch-Site');
+
+        $this->filter->originOnly = false;
+        self::assertTrue($this->filter->beforeAction($this->action));
+    }
+
+    public function testRejectsWhenOriginOnlyAndHeaderInvalid(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'cross-site');
+
+        $this->filter->originOnly = true;
+
+        $this->expectException(BadRequestHttpException::class);
+        $this->filter->beforeAction($this->action);
+    }
+
+    public function testEnforcesWhenCsrfDisabled(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'cross-site');
+
+        $original = $this->request->enableCsrfValidation;
+        $this->request->enableCsrfValidation = false;
+
+        try {
+            $this->filter->originOnly = true;
+            $this->expectException(BadRequestHttpException::class);
+            $this->filter->beforeAction($this->action);
+        } finally {
+            $this->request->enableCsrfValidation = $original;
+        }
+    }
+
+    public function testSkipsSafeMethods(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'GET';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'cross-site');
+
+        $this->filter->originOnly = true;
+        self::assertTrue($this->filter->beforeAction($this->action));
+    }
+
+    public function testInvalidHeaderFallsThroughWhenNotOriginOnly(): void
+    {
+        $_SERVER['REQUEST_METHOD'] = 'POST';
+        $this->request->getHeaders()->set('Sec-Fetch-Site', 'cross-site');
+
+        $this->filter->originOnly = false;
+        self::assertTrue($this->filter->beforeAction($this->action));
+    }
+}