this post was submitted on 09 May 2024
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This just sounds like a bad idea, a solution in search of a problem. Sure, sudo is a setuid binary, but it's a fairly simple program, and at some point, you have to trust the code. It's also a very fundamental piece of the system that you want to always work, even (especially!) when other things get borked. The brief description of run0 already has too many potential points of failure.
Some people would disagree to this.
If the "listener" is PID1, which will run the privileged command, in theory, it would be quite bullet proof (in a working system PID1 is always there). But since this is systemd, PID1 is much more than that and much more complex. On the other hand spawning another daemon from PID1 to be the "listener" makes it, perhaps, even more complicated. You'd have to make sure the listener is always running and have some process supervisor there to watch if it exits... and maybe even a watchdog polling it to make sure it isn't frozen.
So my conclusion is the same as yours:
We already have a working solution. Have a well written SUID program. I've been using doas for some years now. It's simple enough that I trust it.
I've always wondered why we even bother with SUID commands. Why not just log in as root?
On a server, it allows you to track who initiates which root season session. It also greatly minimizes the attack surface from a security perspective to have admin privileged accounts unable to be remotely connected to.
Wouldn't separate SSH keys achieve the same?
Really? How, exactly? Break the ssh key authentication? And wouldn't that apply to all accounts equally?
Separate ssh keys for the user and the admin? Yeah, see point 2, admins should not be remotely accessible.
Keys aren't perfect security. They can easily be mishandled, sometimes getting published to GitHub, copied to USB drives which can easily be lost, etc.
Further, there have been attacks against SSH that let malicious actors connect remotely to any session, or take over existing sessions. By not allowing remote access on privileged accounts, you minimize risk.
Forcing a non privileged remote session to authenticate with a password establishes a second factor of security that is different from the first. This means a cracked password or a lost key is still not enough for a malicious actor to accomplish administrative privileges.
A key is something you have
A password is something you know
So, by not allowing remote privileged sessions, we're forcing a malicious actor to take one more non-trivial step before arriving at their goals. A step that will likely be fairly obvious in logs on a monitored machine.
If I get into your non-privileged account I can set up a program that acts like sudo and I bet 99% of people will never notice they just gave their password away. And even if they do it's too late anyway because I've just compromised root and locked everybody out and I'm in there shitting on the filesystems or whatever. Because root can do anything.
And if I can't break into your non-privileged account then I can't break into a privileged account either.
These artificial distinctions between "non-privileged" and "superuser" accounts need to stop. This is not good security, this is not zero trust. Either you don't trust anybody and enforce explicit privilege escalation for specific things, or just accept that you're using a "super" paradigm and once you've got access to that user all bets are off.
I strongly disagree with your premise. Separating authentication and privilege escalation adds layers of security that are non-trivial and greatly enhance resilience. Many attacks are detected and stopped at privilege escalation, because it happens locally before a user can stop or delete the flow of logs.
No you cannot. A non privileged user doesn't have the access necessary to run a program that can accomplish this.
Once again, you didn't privilege escalate, because once you have a foothold (authentication) you don't have the necessary privileges, so you must perform reconnaissance to identify an exploitable vector to privilage escalate with. This can be any number of things, but it's always noisy and slow, usually easy to detect in logs. There is a reason the most sophisticated attacks against well protected targets are "low and slow".
You're ignoring my points given regarding the risks of compromised keys. If there are no admin keys, there are no remote admin sessions.
Spoken like someone who has never red teamed or purple teamed. Even admin accounts are untrusted, given only privileges specific to their role, and closely monitored. That doesn't mean they should have valid security measures thrown away.
It would be a script called "sudo" somewhere in your PATH. You type sudo, you give it your password, done.
That's called 'privilege escalation', and replacing system level calls with user level calls is closely watched for and guarded against with many different security measures including SELinux.
You've already outed yourself multiple times in this thread as someone who doesn't understand how security in the real world works. Take the L and try to learn from this. It's okay not to understand something. But it's very important to recognize when that happens and not claim to understand better than someone else.
It's not privilege escalation because it doesn't subvert the correct authentication mechanism, it leverages it. This particular technique is called UI input capture. It's a script that shows a password prompt then uses your password to do things as root. Nothing untowards would be detected. The main defense is to always run commands with full path – which nobody does.
Separating the process of reaching root in two steps does nothing to improve security, it actually increases complexity and subverts security. If the system is set up to SSH as root you either have a good key or you don't. If you force people to SSH as individual users and then use a complex mechanism to reach root you create opportunity for a hundred more attack methods, and add a false sense of security.
Input capture btw is not the only method. Sudo has a lot of them. Another very common one is leveraging the password cache timeout.
How about we skip the dick measuring contest and we stick to the discussion at hand.