No direct "universal" download link exists. Any site claiming a one-click link for "ZTE ZXHN F670L EPON firmware without login" is fraudulent.
to act as a mesh network controller compatible with standards. Performance Optimizations : zte zxhn f670l epon firmware link
The following forums have curated lists of clean firmware: No direct "universal" download link exists
If you have obtained a compatible firmware file, the general update process is as follows: zte zxhn f670l epon firmware link