#398

backend/app/services/preview/url_safety.rb

@@ -40,6 +40,8 @@ module Preview
       end
 
       [uri, parsed_addresses.map(&:to_s)]
+    rescue Resolv::ResolvError
+      raise UnsafeUrl, 'URL のホストを解決できません．'
     rescue URI::InvalidURIError, IPAddr::InvalidAddressError
       raise UnsafeUrl, 'URL が不正です．'
     end