Hi all,
I found a hobby in trying to secure my Linux server, maybe even beyond reasonable means.
Currently, my system is heavily locked down with user permissions. Every file has a group owner, and every server application has its own user. Each user will only have access to files it is explicitly added to.
My server is only accessible from LAN or VPN (though I’ve been interested in hosting publicly accessible stuff). I have TLS certs for most everything they can use it (albeit they’re self signed certs, which some people don’t like), and ssh is only via ssh keys that are passphrase protected.
What are some suggestions for things I can do to further improve my security? It doesn’t have to be super useful, as this is also fun for me.
Some things in mind:
- 2 factor auth for SSH (and maybe all shell sessions if I can)
- look into firejail, nsjail, etc.
- look into access control lists
- network namespace and vlan to prevent server applications from accessing the internal network when they don’t need to
- considering containerization, but so far, I find it not worth foregoing the benefits I get of a single package manager for the entire server
Other questions:
- Is there a way for me to be “notified” if shell access of any form is gained by someone? Or somehow block all shell access that is not 2FA’d?
- my system currently secures files on the device. But all applications can see all process PIDs. Do I need to protect against this?
threat model
- attacker gains shell access
- attacker influences server application to perform unauthorized actions
- not in my threat model: physical access
Like others have mentioned, SELinux could be a great addition. It can be a massive pain, but it’s really effective at locking things down (if configured properly).
However, the difficulty will depend on the distro. I use it with Gentoo, which has plenty of support/docs for it and provides policies for many packages. Although (when running strict policy types) I usually end up needing to adjust them or write my own.
Obviously Red Hat would be another good choice, but I haven’t tried it. Fedora also has good support, but I’ve only ever used the OOTB targeted policies.
That said, I’ve started relying on users/groups more often lately, since it really gets in the way of everything.
A fellow gentoo user in the wild! Do you have any thoughts on using containers with gentoo? It pains me the idea of foregoing all the awesome features of portage by using containers.
What exactly does SE Linux provide over users / groups?
👋 right on! I actually also have used containers as a key to my security layout before, but yeah you miss out on all the benefits of portage.
I was doing something crazy and actually running Gentoo inside each one! It was very difficult to stay up-to-date. But I basically had my host as barebones as possible and used LibVirt containers for everything, attempting to make a few templates that I could keep updated and base other VMs on. I was able to keep this up for about two years then I had to relax (was my main PC). But it was really secure, and it does work.
The benefit of encapsulation is that you have a lot of freedom inside each container, like install a different distro if you need to. Also as long as they are isolated you don’t need to worry as much about their individual security. But it’s still good to. I ran SELinux on the host and non-SELinux (but hardened) in the guests.
SELinux has a lot of advantages over users/groups, but I think the latter can be just as secure if you know what you’re doing. For example with SELinux you can prevent certain applications from accessing the network, or restrict access to certain ports, etc. It’s also useful for desktop environments where a lot of GUI apps run under one user- e.g. neither my main user nor any other program can access my keepassxc directory, only the keepassxc process (and root) can (even though the application is running under my main user). You can also restrict root quite a bit, especially if you compile in the option to prevent disabling SELinux at boot (I need to recompile my kernel to disable it).
But again while it is fun to learn, it is quite a pain and I’ve relaxed the setup on my new computer to use a different user for everything (including gui apps), which I think is secure enough for me. But this style relies on my ability to adhere to it, whereas with SELinux you can set it up to where you’re forced to