To clear all misunderstandings written in here: 3DS Max 2018 service pack 4 is accessible to me, even as a single-user Student license holder. It's just really well-hidden in the https://manage.autodesk.com pages, follow these instructions to locate the download:
1) go to https://manage.autodesk.com, logged in
2) do not click "product updates", as the main problem misleading everyone is that it's not there, wrong location
3) go to the correct location: "All products & services" > click 3ds Max 2018 (in my case says: "1 seat, student, single user) and then click "View downloads".
4) in the "view downloads" tab, you select "Updates and add-ons" sub-tab.
Now, you will see the Service Packs like:
3ds Max 2018.4 Update
Update (230.3MB). Released Dec 6, 2017
and carry out a "Browser download", then install the package to your PC.
If anyone still doesn't understand, here are images of each step in navigation through pages (the things you'll have to click will be circled red):
So if you know where to find it, the process is easily done. But the placement (or lack of placement in other places one would expect it) can make it confusing for people so they think it's not offered. This in part is due to it also not being available on https://knowledge.autodesk.com/support/3ds-max/downloads for 3DS 2018, where it was for earlier versions. This may add to the confusion.