diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30a3be0c32c..e20e0091137 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,9 +2,11 @@
 
 ## Unreleased
 
+- Added `craft\services\Security::isSystemDir()`.
 - Fixed a bug where `craft\helpers\StringHelper::lines()` was returning an array of `Stringy\Stringy` objects, rather than strings.
 - Fixed styling issues with Template field layout UI elements’ selector labels.
 - Fixed a validation error that could occur when saving a relational field, if the “Maintain hierarchy” setting had been enabled but was no longer applicable. ([#15666](https://github.com/craftcms/cms/issues/15666))
+- Fixed an information disclosure vulnerability.
 
 ## 4.12.0 - 2024-09-03
 
diff --git a/src/fs/Local.php b/src/fs/Local.php
index d9185146c8a..35bf9ab8914 100644
--- a/src/fs/Local.php
+++ b/src/fs/Local.php
@@ -130,21 +130,8 @@ protected function defineRules(): array
      */
     public function validatePath(string $attribute, ?array $params, InlineValidator $validator): void
     {
-        // Make sure it’s not within any of the system directories
-        $path = FileHelper::absolutePath($this->getRootPath(), '/');
-
-        $systemDirs = Craft::$app->getPath()->getSystemPaths();
-
-        foreach ($systemDirs as $dir) {
-            $dir = FileHelper::absolutePath($dir, '/');
-            if (str_starts_with("$path/", "$dir/")) {
-                $validator->addError($this, $attribute, Craft::t('app', 'Local filesystems cannot be located within system directories.'));
-                break;
-            }
-            if (str_starts_with("$dir/", "$path/")) {
-                $validator->addError($this, $attribute, Craft::t('app', 'Local filesystems cannot be located above system directories.'));
-                break;
-            }
+        if (Craft::$app->getSecurity()->isSystemDir($this->getRootPath())) {
+            $validator->addError($this, $attribute, Craft::t('app', 'Local filesystems cannot be located within or above system directories.'));
         }
     }
 
diff --git a/src/helpers/Html.php b/src/helpers/Html.php
index 927e3c6d1d4..10f97ced2ae 100644
--- a/src/helpers/Html.php
+++ b/src/helpers/Html.php
@@ -990,11 +990,22 @@ public static function dataUrl(string $file, ?string $mimeType = null): string
             throw new InvalidArgumentException("Invalid file path: $file");
         }
 
+        $file = FileHelper::absolutePath(Craft::getAlias($file), '/');
+
+        if (Craft::$app->getSecurity()->isSystemDir(dirname($file))) {
+            throw new InvalidArgumentException(sprintf('%s cannot be passed a path within or above system directories.', __METHOD__));
+        }
+
+        $ext = pathinfo($file, PATHINFO_EXTENSION);
+        if (strtolower($ext) === 'php') {
+            throw new InvalidArgumentException(sprintf('%s cannot be passed a path to a PHP file.', __METHOD__));
+        }
+
         if ($mimeType === null) {
             try {
                 $mimeType = FileHelper::getMimeType($file);
             } catch (Throwable $e) {
-                Craft::warning("Unable to determine the MIME type for $file: " . $e->getMessage());
+                Craft::warning("Unable to determine the MIME type for $file: " . $e->getMessage(), __METHOD__);
                 Craft::$app->getErrorHandler()->logException($e);
             }
         }
diff --git a/src/services/Security.php b/src/services/Security.php
index df065c27f2b..ae3c34691b5 100644
--- a/src/services/Security.php
+++ b/src/services/Security.php
@@ -8,6 +8,7 @@
 namespace craft\services;
 
 use Craft;
+use craft\helpers\FileHelper;
 use yii\base\Exception;
 use yii\base\InvalidArgumentException;
 use yii\base\InvalidConfigException;
@@ -196,4 +197,25 @@ public function redactIfSensitive(string $key, mixed $value): mixed
 
         return $value;
     }
+
+    /**
+     * Returns whether the given file path is located within or above any system directories.
+     *
+     * @param string $path
+     * @return bool
+     * @since 4.12.1
+     */
+    public function isSystemDir(string $path): bool
+    {
+        $path = FileHelper::absolutePath($path, '/');
+
+        foreach (Craft::$app->getPath()->getSystemPaths() as $dir) {
+            $dir = FileHelper::absolutePath($dir, '/');
+            if (str_starts_with("$path/", "$dir/") || str_starts_with("$dir/", "$path/")) {
+                return true;
+            }
+        }
+
+        return false;
+    }
 }
diff --git a/src/translations/en/app.php b/src/translations/en/app.php
index f33f0f15cbe..aa97a41834b 100644
--- a/src/translations/en/app.php
+++ b/src/translations/en/app.php
@@ -855,8 +855,7 @@
     'Loading' => 'Loading',
     'Local Folder' => 'Local Folder',
     'Local copies of remote images, generated thumbnails' => 'Local copies of remote images, generated thumbnails',
-    'Local filesystems cannot be located above system directories.' => 'Local filesystems cannot be located above system directories.',
-    'Local filesystems cannot be located within system directories.' => 'Local filesystems cannot be located within system directories.',
+    'Local filesystems cannot be located within or above system directories.' => 'Local filesystems cannot be located within or above system directories.',
     'Localizing relations' => 'Localizing relations',
     'Location' => 'Location',
     'Locations that should be available for previewing entries in this section.' => 'Locations that should be available for previewing entries in this section.',
diff --git a/src/web/twig/Extension.php b/src/web/twig/Extension.php
index a11f6400d98..72d399cff9d 100644
--- a/src/web/twig/Extension.php
+++ b/src/web/twig/Extension.php
@@ -1437,11 +1437,16 @@ public function collectFunction(mixed $var): Collection
      */
     public function dataUrlFunction(Asset|string $file, ?string $mimeType = null): string
     {
-        if ($file instanceof Asset) {
-            return $file->getDataUrl();
-        }
+        try {
+            if ($file instanceof Asset) {
+                return $file->getDataUrl();
+            }
 
-        return Html::dataUrl(Craft::getAlias($file), $mimeType);
+            return Html::dataUrl(Craft::getAlias($file), $mimeType);
+        } catch (InvalidArgumentException $e) {
+            Craft::warning($e->getMessage(), __METHOD__);
+            return '';
+        }
     }
 
     /**