symfony
diff --git a/‎src/Symfony/Component/Routing/Loader/Psr4DirectoryLoader.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Routing/Loader/Psr4DirectoryLoader.php
+5Lines changed: 5 additions & 0 deletions b/‎src/Symfony/Component/Routing/Loader/Psr4DirectoryLoader.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Routing/Loader/Psr4DirectoryLoader.php
+5Lines changed: 5 additions & 0 deletions
diff --git a/‎src/Symfony/Component/Routing/Tests/Loader/Psr4DirectoryLoaderTest.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Routing/Tests/Loader/Psr4DirectoryLoaderTest.php
+29Lines changed: 29 additions & 0 deletions b/‎src/Symfony/Component/Routing/Tests/Loader/Psr4DirectoryLoaderTest.php
Copy file name to clipboardExpand all lines: src/Symfony/Component/Routing/Tests/Loader/Psr4DirectoryLoaderTest.php
+29Lines changed: 29 additions & 0 deletions
@@ -15,6 +15,7 @@
 use Symfony\Component\Config\Loader\DirectoryAwareLoaderInterface;
 use Symfony\Component\Config\Loader\Loader;
 use Symfony\Component\Config\Resource\DirectoryResource;
+use Symfony\Component\Routing\Exception\InvalidArgumentException;
 use Symfony\Component\Routing\RouteCollection;
 
 /**
@@ -43,6 +44,10 @@ public function load(mixed $resource, ?string $type = null): ?RouteCollection
             return new RouteCollection();
         }
 
+        if (!preg_match('/^(?:[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*+\\\)++$/', trim($resource['namespace'], '\\').'\\')) {
+            throw new InvalidArgumentException(\sprintf('Namespace "%s" is not a valid PSR-4 prefix.', $resource['namespace']));
+        }
+
         return $this->loadFromDirectory($path, trim($resource['namespace'], '\\'));
     }
 
 
@@ -15,6 +15,7 @@
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\Config\Loader\DelegatingLoader;
 use Symfony\Component\Config\Loader\LoaderResolver;
+use Symfony\Component\Routing\Exception\InvalidArgumentException;
 use Symfony\Component\Routing\Loader\AttributeClassLoader;
 use Symfony\Component\Routing\Loader\Psr4DirectoryLoader;
 use Symfony\Component\Routing\Route;
@@ -90,6 +91,34 @@ public static function provideNamespacesThatNeedTrimming(): array
         ];
     }
 
+    /**
+     * @dataProvider provideInvalidPsr4Namespaces
+     */
+    public function testInvalidPsr4Namespace(string $namespace, string $expectedExceptionMessage)
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage($expectedExceptionMessage);
+
+        $this->getLoader()->load(
+            ['path' => 'Psr4Controllers', 'namespace' => $namespace],
+            'attribute'
+        );
+    }
+
+    public static function provideInvalidPsr4Namespaces(): array
+    {
+        return [
+            'slash instead of back-slash' => [
+                'namespace' => 'App\Application/Controllers',
+                'exceptionMessage' => 'Namespace "App\Application/Controllers" is not a valid PSR-4 prefix.',
+            ],
+            'invalid namespace' => [
+                'namespace' => 'App\Contro llers',
+                'exceptionMessage' => 'Namespace "App\Contro llers" is not a valid PSR-4 prefix.',
+            ],
+        ];
+    }
+
     private function loadPsr4Controllers(): RouteCollection
     {
         return $this->getLoader()->load(