Error: failed to open dir: Permission denied in RecursiveDirectoryIterator

RecursiveDirectoryIterator->__construct('/home/admin/web/123.com/public_html', 12816) (Line: 421)
Drupal\Core\Extension\ExtensionDiscovery->scanDirectory('', ) (Line: 205)
Drupal\Core\Extension\ExtensionDiscovery->scan('module') (Line: 170)
Drupal\Core\Config\InstallStorage->getAllFolders() (Line: 95)
Drupal\Core\Config\InstallStorage->exists('core.extension') (Line: 103)
Drupal\Core\Config\FileStorage->read('core.extension') (Line: 130)
Drupal\Core\Config\FileStorage->readMultiple(Array) (Line: 165)
Drupal\Core\Config\ConfigFactory->doLoadMultiple(Array, 1) (Line: 104)
Drupal\Core\Config\ConfigFactory->doGet('core.extension') (Line: 89)
Drupal\Core\Config\ConfigFactory->get('core.extension') (Line: 220)
Drupal\Core\Extension\ThemeHandler->refreshInfo() (Line: 186)
Drupal\Core\Extension\ThemeHandler->listInfo() (Line: 65)
_drupal_maintenance_theme() (Line: 710)
drupal_maintenance_theme() (Line: 967)
install_display_output(Array, Array, Array) (Line: 264)
_drupal_log_error(Array, 1) (Line: 570)
_drupal_exception_handler(Object)

What is the proper fix for this?