If you are looking for a stable and secure experience, you should use a release.
That means:
Various third-party sites like the Internet Archive host legacy snapshots for historical or testing purposes. ubuntu 1710 download
You should use Ubuntu 17.10 as a daily driver or on any production system. If you are looking for a stable and
If you understand the risks and still need the ISO for offline/legacy purposes, here’s where to find it: ubuntu 1710 download
http://old-releases.ubuntu.com/releases/17.10/
On that page, look for: