404 a null byte or a directory on the showcase's asset route

Plan step 38 review: a %00 in the asset path reached realpath(), which
throws on a null byte, so the route answered 500 instead of 404; a
directory whose name ended in a served extension would have reached
response()->file(). Both 404 now. The tests add what the review
probed: encoded dot segments and slashes, backslashes, absolute paths,
a directory, a very long path and a symbolic link pointing out of a
served folder, all 404.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

src/Http/Controllers/ShowcaseAssetController.php

@@ -69,12 +69,16 @@ class ShowcaseAssetController
     }
 
     /**
-     * A font or an SVG the stylesheet's `url()`s point at, MIME-typed by extension: `..` and
+     * A font or an SVG the stylesheet's `url()`s point at, MIME-typed by extension. The path is
-     * anything the two folders above do not contain resolves to nothing and 404s, the same as an
+     * resolved on disk first, so `..` (however it was encoded), a symbolic link and anything else
-     * unlisted extension (the font's own `OFL.txt`, sitting right beside it, included).
+     * that lands outside the two folders above 404s, as does a directory, a null byte (which
+     * `realpath()` would throw on) and an unlisted extension (the font's own `OFL.txt`, sitting
+     * right beside it, included).
      */
     public function file(string $path): BinaryFileResponse
     {
+        abort_if(str_contains($path, "\0"), 404);
+
         $segments = explode('/', $path, 2);
         $folder = $segments[0] ?? null;
         $rest = $segments[1] ?? null;
@@ -84,7 +88,7 @@ class ShowcaseAssetController
         $root = realpath(dirname(__DIR__, 3)."/resources/{$folder}");
         $real = $root === false ? false : realpath("{$root}/{$rest}");
 
-        abort_unless($real !== false && str_starts_with($real, $root.DIRECTORY_SEPARATOR), 404);
+        abort_unless($real !== false && str_starts_with($real, $root.DIRECTORY_SEPARATOR) && is_file($real), 404);
 
         $mime = self::MIME_TYPES[strtolower(pathinfo($real, PATHINFO_EXTENSION))] ?? null;
 

tests/Feature/ShowcaseAssetsTest.php

@@ -54,6 +54,31 @@ it('404s a path that climbs out of the two served folders', function () {
     $this->get('/material/assets/fonts/../../composer.json')->assertNotFound();
 });
 
+it('404s every other way out of the two served folders', function (string $path) {
+    $this->get('/material/assets/'.$path)->assertNotFound();
+})->with([
+    'encoded dot segments' => 'fonts/%2e%2e/%2e%2e/composer.json',
+    'encoded slashes' => 'fonts/..%2f..%2fcomposer.json',
+    'backslashes' => 'fonts/google-sans-flex/..%5c..%5c..%5ccomposer.json',
+    'an absolute path' => '/etc/hosts',
+    'an absolute path inside a folder' => 'fonts//etc/hosts',
+    'a null byte' => 'fonts/google-sans-flex/GoogleSansFlex-Latin.woff2%00.txt',
+    'a directory' => 'svg/symbols',
+    'a folder itself' => 'fonts/',
+    'a very long path' => 'fonts/'.str_repeat('a/', 3000).'x.woff2',
+]);
+
+it('404s a symbolic link inside a served folder that points out of it', function () {
+    $link = __DIR__.'/../../resources/svg/showcase-assets-test-link.svg';
+    symlink(realpath(__DIR__.'/../../composer.json'), $link);
+
+    try {
+        $this->get('/material/assets/svg/showcase-assets-test-link.svg')->assertNotFound();
+    } finally {
+        unlink($link);
+    }
+});
+
 it('404s a folder the showcase does not serve', function () {
     $this->get('/material/assets/css/all.css')->assertNotFound();
 });