diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7a98fce..6d0be45 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,7 +11,7 @@ on:
 
 jobs:
   testsuite:
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-24.04
     strategy:
       fail-fast: false
       matrix:
diff --git a/src/Twig/Extension/UtilsExtension.php b/src/Twig/Extension/UtilsExtension.php
index 91a7ce7..08f9136 100644
--- a/src/Twig/Extension/UtilsExtension.php
+++ b/src/Twig/Extension/UtilsExtension.php
@@ -20,6 +20,7 @@
 
 use Twig\Extension\AbstractExtension;
 use Twig\TwigFilter;
+use function Cake\Core\deprecationWarning;
 
 /**
  * Class UtilsExtension.
@@ -34,8 +35,16 @@ class UtilsExtension extends AbstractExtension
     public function getFilters(): array
     {
         return [
-            new TwigFilter('serialize', 'serialize'),
-            new TwigFilter('unserialize', 'unserialize'),
+            new TwigFilter('serialize', function (string $value): mixed {
+                deprecationWarning('5.0.2', 'Usage of serialize in templates deprecated.');
+
+                return serialize($value);
+            }),
+            new TwigFilter('unserialize', function (string $value): mixed {
+                deprecationWarning('5.0.2', 'unserialize is deprecated. Its usage creates arbitrary object deserialization issues');
+
+                return unserialize($value, ['allowed_classes' => false]);
+            }),
             new TwigFilter('md5', 'md5'),
             new TwigFilter('base64_encode', 'base64_encode'),
             new TwigFilter('base64_decode', 'base64_decode'),
diff --git a/src/Twig/FileLoader.php b/src/Twig/FileLoader.php
index 5874766..19af51c 100644
--- a/src/Twig/FileLoader.php
+++ b/src/Twig/FileLoader.php
@@ -92,8 +92,26 @@ public function exists(string $name)
      */
     public function findTemplate(string $name): string
     {
+        $templatePaths = App::path('templates');
         if (file_exists($name)) {
-            return $name;
+            $name = str_replace('//', '/', $name);
+            // Check both app template paths and all plugins,
+            // as template from element() end up here too.
+            // We also need to protect against `{% include var_name %}`
+            // where var_name is request data.
+            foreach ($templatePaths as $templatePath) {
+                if (str_starts_with($name, $templatePath)) {
+                    return $name;
+                }
+            }
+            foreach (Plugin::loaded() as $pluginName) {
+                $pluginPath = Plugin::templatePath($pluginName);
+                if (str_starts_with($name, $pluginPath)) {
+                    return $name;
+                }
+            }
+
+            throw $this->loaderError($name, $templatePaths);
         }
 
         [$plugin, $name] = pluginSplit($name);
@@ -105,24 +123,35 @@ public function findTemplate(string $name): string
             if ($path !== null) {
                 return $path;
             }
-
             $error = "Could not find template `{$name}` in plugin `{$plugin}` in these paths:\n\n"
                 . "- `{$templatePath}`\n";
             throw new LoaderError($error);
         }
 
-        foreach (App::path('templates') as $templatePath) {
+        foreach ($templatePaths as $templatePath) {
             $path = $this->checkExtensions($templatePath . $name);
             if ($path !== null) {
                 return $path;
             }
         }
+        throw $this->loaderError($name, $templatePaths);
+    }
 
+    /**
+     * Create a LoaderError with template path list in the message.
+     *
+     * @param string $name The name of the template that could not be found.
+     * @param array $templatePaths List of template paths that were searched
+     * @return \Twig\Error\LoaderError
+     */
+    protected function loaderError(string $name, array $templatePaths): LoaderError
+    {
         $error = "Could not find template `{$name}` in these paths:\n\n";
-        foreach (App::path('templates') as $templatePath) {
+        foreach ($templatePaths as $templatePath) {
             $error .= "- `{$templatePath}`\n";
         }
-        throw new LoaderError($error);
+
+        return new LoaderError($error);
     }
 
     /**
diff --git a/tests/TestCase/Twig/Extension/UtilsExtensionTest.php b/tests/TestCase/Twig/Extension/UtilsExtensionTest.php
new file mode 100644
index 0000000..e574895
--- /dev/null
+++ b/tests/TestCase/Twig/Extension/UtilsExtensionTest.php
@@ -0,0 +1,55 @@
+<?php
+declare(strict_types=1);
+
+/**
+ * CakePHP(tm) : Rapid Development Framework (https://cakephp.org)
+ * Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
+ * Copyright (c) 2014 Cees-Jan Kiewiet
+ *
+ * Licensed under The MIT License
+ * For full copyright and license information, please see the LICENSE.txt
+ * Redistributions of files must retain the above copyright notice
+ *
+ * @copyright     Copyright (c) Cake Software Foundation, Inc. (https://cakefoundation.org)
+ * @link          https://cakephp.org CakePHP(tm) Project
+ * @since         1.0.0
+ * @license       https://opensource.org/licenses/mit-license.php MIT License
+ */
+
+namespace Cake\TwigView\Test\TestCase\Twig\Extension;
+
+use Cake\TwigView\Twig\Extension\UtilsExtension;
+use TestApp\GadgetMarker;
+use Twig\Environment;
+use Twig\Loader\ArrayLoader;
+
+class UtilsExtensionTest extends AbstractExtensionTest
+{
+    public function setUp(): void
+    {
+        parent::setUp();
+        $this->extension = new UtilsExtension();
+    }
+
+    public function testUnserializePreventObject(): void
+    {
+        $this->skipIf(PHP_VERSION_ID < 80300, 'Requires PHP8.3 or higher');
+
+        $twig = new Environment(new ArrayLoader([
+            // {% set %} so we exercise the filter without stringifying the result.
+            'object' => '{% set _ = payload|unserialize %}(rendered)',
+            'array' => '{{ (payload|unserialize)["role"] }}',
+        ]));
+        $twig->addExtension(new UtilsExtension());
+
+        // 1) Object payload: does a gadget's magic method run?
+        GadgetMarker::$woken = false;
+        $this->deprecated(function () use ($twig): void {
+            $twig->render('object', ['payload' => serialize(new GadgetMarker())]);
+            $this->assertFalse(GadgetMarker::$woken, 'Should not have modified GadgetMarker');
+
+            $out = $twig->render('array', ['payload' => serialize(['role' => 'editor'])]);
+            $this->assertStringContainsString('editor', $out);
+        });
+    }
+}
diff --git a/tests/TestCase/Twig/FileLoaderTest.php b/tests/TestCase/Twig/FileLoaderTest.php
index dcfdff2..fd289ed 100644
--- a/tests/TestCase/Twig/FileLoaderTest.php
+++ b/tests/TestCase/Twig/FileLoaderTest.php
@@ -81,13 +81,14 @@ public function testGetCacheKeyPluginNonExistingFile()
 
     public function testIsFresh()
     {
-        file_put_contents(TMP . 'TwigViewIsFreshTest', 'TwigViewIsFreshTest');
-        $time = filemtime(TMP . 'TwigViewIsFreshTest');
+        $path = TEST_APP . 'templates/test_is_fresh.twig';
+        file_put_contents($path, 'is fresh test');
+        $time = filemtime($path);
 
-        $this->assertTrue($this->loader->isFresh(TMP . 'TwigViewIsFreshTest', $time + 5));
-        $this->assertTrue(!$this->loader->isFresh(TMP . 'TwigViewIsFreshTest', $time - 5));
+        $this->assertTrue($this->loader->isFresh($path, $time + 5));
+        $this->assertTrue(!$this->loader->isFresh($path, $time - 5));
 
-        unlink(TMP . 'TwigViewIsFreshTest');
+        unlink($path);
     }
 
     public function testIsFreshNonExistingFile()
diff --git a/tests/TestCase/View/TwigViewTest.php b/tests/TestCase/View/TwigViewTest.php
index 13bf538..63e1762 100644
--- a/tests/TestCase/View/TwigViewTest.php
+++ b/tests/TestCase/View/TwigViewTest.php
@@ -20,6 +20,7 @@
 
 use Cake\TestSuite\TestCase;
 use TestApp\View\AppView;
+use Twig\Error\LoaderError;
 use Twig\Error\RuntimeError;
 use Twig\Error\SyntaxError;
 use Twig\Extra\Markdown\DefaultMarkdown;
@@ -242,6 +243,17 @@ public function testThrowSyntaxError()
         $this->view->render('syntaxerror', false);
     }
 
+    public function testTemplatePathRestriction()
+    {
+        $path = TMP . 'secret.txt';
+        file_put_contents($path, 'SECRET DATA from /tmp/secret.txt');
+        $view = new AppView();
+        $view->set('item', $path);
+        $this->expectException(LoaderError::class);
+        $this->expectExceptionMessage('Could not find template');
+        $view->render('template_path_restriction');
+    }
+
     public function testHelperFunction()
     {
         $view = new AppView(null, null, null, [
diff --git a/tests/test_app/src/GadgetMarker.php b/tests/test_app/src/GadgetMarker.php
new file mode 100644
index 0000000..a159879
--- /dev/null
+++ b/tests/test_app/src/GadgetMarker.php
@@ -0,0 +1,15 @@
+<?php
+declare(strict_types=1);
+
+namespace TestApp;
+
+class GadgetMarker
+{
+    public static bool $woken = false;
+
+    public function __wakeup(): void
+    {
+        self::$woken = true;
+        echo "  [!] GadgetMarker::__wakeup fired during unserialize (object injection)\n";
+    }
+}
diff --git a/tests/test_app/templates/template_path_restriction.twig b/tests/test_app/templates/template_path_restriction.twig
new file mode 100644
index 0000000..c672344
--- /dev/null
+++ b/tests/test_app/templates/template_path_restriction.twig
@@ -0,0 +1,5 @@
+{#
+Ensure that `include` applies template path restriction, so that user data + include don't open
+up arbitrary file reads.
+#}
+{% include item %}
\ No newline at end of file