A Path Traversal vulnerability in Controllers/LetsEncryptController.cs in LetsEncryptController in GrandNode 4.40 allows remote, unauthenticated attackers to retrieve arbitrary files on the web server via specially crafted LetsEncrypt/Index?fileName= HTTP requests. A patch for this issue was made on 2019-05-30 in GrandNode 4.40.
https://github.com/grandnode/grandnode
http://packetstormsecurity.com/files/153373/GrandNode-4.40-Path-Traversal-File-Download.html