Edit/Solved: Thank you for all the great input! Both on alternative solutions and on security implications. I’m going to make a draft on how I would setup the e-mail method as securely as possible as a programming/scripting exercise, but will IRL probably end up using either some reverse tunnel/shell variant.
Edit 2: or, as a hardware solution, install an extra NIC that I expose to the opennet - thus enabling remote port forwarding - while binding all my sensitive processes/traffic to my encrypted NIC.
I cannot ssh into my Linux box from outside of my LAN since I’m behind a VPN that doesn’t support port forwarding. Is it possible to make my Linux box receive, interpret and execute commands through e-mail instead? I’ve tried looking for answers through DuckDuckGo’s search engine, to no avail. If I may dream, I would like to setup an e-mail server with a systemd service or just run a script that continuously downloads the emails, prints their content to stdin and executes, perhaps through command substitution, whatever is in stdin.
It’s possible—I’ve used Perl scripts to pull data automatically out of email attachments stored in a maildir setup, and you should be able to pick commands out of a plain-text email body with a scripting language even more easily—but I will add my voice to the chorus that’s saying you should look into any other method you can find before settling on this. If it turns out you must proceed along these lines, think long and hard about security.