If this sounds too complex, the device is e-waste. Buy a replacement.
ZTE Zxhn F670l Firmware v1. 1.10p1n2e security vulnerabilities, CVEs. ZTE » Zxhn F670l Firmware » v1. 1.10p1n2e (Operating system) CVE Details
: V1.1.10P1N2E is a widely cited version, though it has documented security vulnerabilities (CVE-2020-6879). V9.0 Series
or tech forums. These are used at your own risk, as incorrect firmware can "brick" the device. The ISP Lock Problem
Only use firmware obtained from your Internet Service Provider (ISP) or a verified official ZTE channel (which is rare for end-users).
If you are experiencing specific bugs (e.g., Wi-Fi dropouts, IPv6 issues, USB sharing failures), it may be worth waiting for an automatic ISP push rather than risking a manual flash. When in doubt, a stable but slightly outdated ONT is far better than a bricked one.
The following versions have been documented for various hardware revisions: V9.0 Series