Issue #3057314 by alexpott, chr.fritsch, larowlan: Harden hash checking in core

core/includes/bootstrap.inc

@@ -679,7 +679,7 @@ function drupal_valid_test_ua($new_prefix = NULL) {
     $test_hmac = Crypt::hmacBase64($check_string, $key);
     // Since we are making a local request a 600 second time window is allowed,
     // and the HMAC must match.
-    if ($time_diff >= 0 && $time_diff <= 600 && $hmac === $test_hmac) {
+    if ($time_diff >= 0 && $time_diff <= 600 && Crypt::hashEquals($test_hmac, $hmac)) {
       $test_prefix = $prefix;
     }
     else {

core/modules/file/src/Element/ManagedFile.php

@@ -110,7 +110,8 @@ public static function valueCallback(&$element, $input, FormStateInterface $form
                 // token added by $this->processManagedFile().
                 elseif (\Drupal::currentUser()->isAnonymous()) {
                   $token = NestedArray::getValue($form_state->getUserInput(), array_merge($element['#parents'], ['file_' . $file->id(), 'fid_token']));
-                  if ($token !== Crypt::hmacBase64('file-' . $file->id(), \Drupal::service('private_key')->get() . Settings::getHashSalt())) {
+                  $file_hmac = Crypt::hmacBase64('file-' . $file->id(), \Drupal::service('private_key')->get() . Settings::getHashSalt());
+                  if ($token === NULL || !Crypt::hashEquals($file_hmac, $token)) {
                     $force_default = TRUE;
                     break;
                   }

core/modules/image/src/Controller/ImageStyleDownloadController.php

@@ -109,7 +109,7 @@ public function deliver(Request $request, $scheme, ImageStyleInterface $image_st
     // starts with styles/.
     $valid = !empty($image_style) && $this->streamWrapperManager->isValidScheme($scheme);
     if (!$this->config('image.settings')->get('allow_insecure_derivatives') || strpos(ltrim($target, '\/'), 'styles/') === 0) {
-      $valid &= $request->query->get(IMAGE_DERIVATIVE_TOKEN) === $image_style->getPathToken($image_uri);
+      $valid &= Crypt::hashEquals($image_style->getPathToken($image_uri), $request->query->get(IMAGE_DERIVATIVE_TOKEN, ''));
     }
     if (!$valid) {
       // Return a 404 (Page Not Found) rather than a 403 (Access Denied) as the

core/modules/system/src/Controller/EntityAutocompleteController.php

@@ -87,7 +87,7 @@ public function handleAutocomplete(Request $request, $target_type, $selection_ha
       $selection_settings = $this->keyValue->get($selection_settings_key, FALSE);
       if ($selection_settings !== FALSE) {
         $selection_settings_hash = Crypt::hmacBase64(serialize($selection_settings) . $target_type . $selection_handler, Settings::getHashSalt());
-        if ($selection_settings_hash !== $selection_settings_key) {
+        if (!Crypt::hashEquals($selection_settings_hash, $selection_settings_key)) {
           // Disallow access when the selection settings hash does not match the
           // passed-in key.
           throw new AccessDeniedHttpException('Invalid selection settings key.');