Linux

You need a legal solution, not a technical.

What you're asking for is an mdm solution, but once a user has access to data, that user can copy it whether you like it or not, whatever mdm solution you use.

Even if you lock down everything, break the USB ports physically, I can photograph the screen, for example.

This has been an age old problem and honestly mdm tools are kind of a hammer where you need a screw driver. It advertises a lack of trust on your end, adds a lot of complexity and potential usability problems and in the end will still never be able to protect you 100%

Go for a legal option and find people you can trust. Also know that 100% security does not exist. The only 100% secure computer is off and on fire.

You need to find someone you trust. There's no technology that can prevent someone disclosing data if it's their job to work with that data.

If you treat people with respect and pay them well, you will be amazed at what they give back. Especially autistic people, they tend to have high personal integrity.

I second the idea that this is a bad idea, but...

Maybe a remote desktop solution is what you want, keep your data local or in your cloud account and provide remote access to a machine that can use it?

You could roll your own self destruct script that will wipe the machine on boot if it hasn't phoned home in a while. You would want to lock the bios and use secure boot. Qubes may have some relevant features.

Also, consider getting a Chromebook instead. ChromeOS is already a walled garden and I think they are remote wipeable and they can run a Linux vm supported by elgoog.

MacOS + JAMF or similar

You'll first want to lock down the laptop with using the TPM so it only boots kernels signed by you, and also encrypt the drive using the TPM as the locking key so the key is only ever available to a kernel you signed. From there you'll probably want to use dm-verity to also verify the integrity of the system or at least during the boot process.

Then, on top of that, once online and the machine is still authorized to access that data, you download a key from a server under your control to unlock the rest of the drive (as another partition). And log those accesses of course.

Then, when you want to revoke access to it, all you have to do is stop replying with the key whenever requested. That just puts a ton of hurdles to overcome to access the data once the server stops handing the key. They would have to pry out the key from the TPM to unlock the first stage and even be able to see how it works and how to potentially obtain the key. They could still manage to copy the data out while the system is fully unlocked and still trusted, which you can make a lot harder by preventing access to external drives or network shares. But they have physical access so they kind of have the last word if they really really really want to exfiltrate data.

This is the best you can do because it's a passive: you stop supplying the unlock key so it's stuck locked encrypted with no key, so the best they can do is format the laptop and sell it or use it for themselves. Any sort of active command system can be pretty easy to counter: just don't get it online if you suspect the kill signal is coming, and it will never come, and therefore never get wiped. You want that system to be wiped by default unless your server decides it's not.

If the data is sensitive just give them a cheap whatever machine and have them connect to a vdi. That way the data never leaves your estate and means you don't have to worry as much about the device being lost/stolen. If this isn't an option I'd strongly recommend looking into an MDM solution for your devices.

There is a fundamental issue with this approach: the rogue employee has already copied the data to a USB drive by the time you try to wipe it.

If the data is confidential, you either need to set up standard disk encryption and trust the employee, or not let them access it in a way it can be bulk copied. For instance, might it be possible for them to use a webapp that you control access to or a remote desktop type setup?

Realistically the best option here is to not have the data in the laptop. So they would remote into a machine you control to access the data, or something of the sort. Regardless the laptop should have full disk encryption so if it gets stolen no data is accidentally leaked.

Other than that the best way I can think of is giving the user a non-root account and have the laptop connect to tailscale automatically so you can always ssh into it and control it if needed. But this is not ideal, because a malicious person could just not connect to the internet and completely block you from doing anything. This is true for almost any sort of remote management tool you would be able to find.

ScaleFusion does this.

As someone else said, I'd go with an MDM vendor instead of trying to build something yourself.

The most secure thing would be to have the person connect to a remote server and do all their work on the remote server, essentially just using the laptop like a thin client.

However, if something goes wrong, and they do the wrong thing, we want to be able to send out some kind of command or similar, that will completely lock, block, or wipe the sensitive data.

You're assuming you'll have a network connection and that sensitive data is all in the same place.

Short of remotely unlocking an encrypted disk on every single boot... and even then...

The best option is to never trust anyone. Depending on how the info is supposed to be used, you can setup a website that does those important things with the sensitive data (stored on the server) without exposing the sensitive data to the user.

VM behind a VPN with a firewall that blocks everything except the rdp protocol and no sudo access?

Fundamentally, once someone has some of the data, they have that data, and you can make no guarantees to remove it. The main question you need to ask is whether or not you're okay with limiting it to the data they've already seen, and what level of technical expertise they need to have to keep the data.

Making some assumptions for what's acceptable as a possibility, and how much you want to invest, I'd recommend having the data on a network-mapped share, and put a daily enforced quota for their access to it. Any data they accessed (presumably as part of their normal duties) is their's, and is "gone." But if you remove their access, they can't get any new data they didn't touch before, and if they were to try and hoover up all the data at some point to copy it off, they'd hit their quota and lose access for a bit (and potentially send you an alert as well). This wouldn't prevent them from slowly sucking out the data day after day.

If they only need to touch a small fraction of the customer data, and particularly if the sensitivity of the data goes down over time (data from a year ago is less sensitive than data from a day ago) this might be a decent solution. If they need to touch a large portion of the data, this isn't as useful.

Edit: another nice bit is that you could log on the network share (at your location) which of the customer data they're accessing and when. If you ever want to audit, and see them accessing things they don't need, you can take action.

I think the next best solution is the VDI one, where you run a compute at your location, and they have to remote into it. If they screen capture, they'll still save off whatever data they access, and if they have poor, or inconsistent, connection up your network it'll affect their ability to do their job (and depending how far away they are it might just be super annoying dealing with the lag). On top of that, it's dependent on how locked-down they need to be to do their job. If they need general Internet access, they could always attempt to upload the data somewhere else for them to pull it. If your corporate network has monitoring to catch that, you might be okay, but otherwise I think it's a lot of downside with a fairly easy way to circumvent.