Do a search for you server OS + STIG
Then, for each service you’re hosting on that server, do a search for:
Service/Program name + STIG/Benchmark
There’s tons of work already done by the vendors in conjunction with the DoD (and CIS) to create lists of potential vulnerable settings that can be corrected before deploying the server.
Along with this, you can usually find scripts and/or Ansible playbooks that will do most of the hardening for you. Though it’s a good Idea to understand what you do and do not need done.
Stumbled uppon this guide
https://github.com/imthenachoman/How-To-Secure-A-Linux-Server
I think its a good place to start
Ask yourself a few questions first before following the massive amount of suggestions and then locking yourself out and so on.
- What are you worried about ?
- How important is your stuff ?
- Make backups and check them
Still worried ? Then there’s the easy way out : Hire some security auditor to help you find holes you left.
- fail2ban / brute forcing prevention
- quick, frequent updates(!)
- containerization / virtualization
- secure passwords, better keys
- firewall
- a hardened operating system (distribution)
- SELinux / Apparmor / … / OpenBSD
- not installing unnecessary stuff
- An admin who is an expert and knows what they do.
Me, two+ decades into tinkering and still a dumbass: “look at me, I’m the expert admin now”
I like to require access to 22 via IP whitelist and all services on SSL behind a reverse proxy. Doesn’t leave much surface to attack.
Also, move ssh to a different, higher port. Since ssh isn’t exactly for noobs, changing the port is easy enough to work with and that alone already reduces port scans and what not
I recently setup Guacamole (Web based VNC/RDP/SSH) with totp and was able to close external SSH access. Now everything I run can sit behind a single reverse proxy, no extra ports.
fail2ban
… is an intrusion prevention software framework. Written in the Python programming language, it is designed to prevent brute-force attacks. It is able to run on POSIX systems that have an interface to a packet-control system or firewall installed locally, such as iptables or TCP Wrapper.
Don’t expose anything to the Internet that you don’t absolutely have to. If you can, put everything behind a VPN gateway.
Make backups. Follow the 3-2-1 rule.
Will a wireguard docker image work for getting ssh access to my server?
I wouldn’t recommend putting ssh behind any vpn connection unles you have a secondary access to the machine (for example virtual tty/terminal from your provider or local network ssh). At best, ssh should be the only publicly accessible service (unless hosting other services that need to be public accessible).
I usually move the ssh port to some higher number just to get rid of the basic scanners/skiddies.
Also disable password login (only keys) and no root login.
And for extra hardening, explicitly allow ssh for only users that need it (in sshd config).
Ssh behind a wire guard VPN server is technically more secure if you don’t have a key-only login, but a pain if the container goes down or if you need to access the server without access to wireguards VPN client on your device.
Highly recommend getting a router that can accept wireguard connections. If the router goes down you’re not accessing anything anyways.
Then always put ssh behind the wireguard connections.
For a homelab, there is rarely a need to expose ssh directly so best practice will always be to have multi layered security when possible.
Move services away from known ports and don’t use ports that end with well known port numbers (22,80,443).
Moving ssh from 22 to 2222 or 443 to 10443 does nothing. You have ~65000 ports. Pick something random like 6744 or 2458
Changing ports does nothing except reduced log chatter.
Security through obscurity is not securityMoving ports does help. It is not a sure thing but when used in conjunction with other security mechanism can help get rid the of the low hanging fruit of scriptkiddies and automated scans.
Security by obscurity is no security.
It is if you are defending against automation.
It defends against the lowest level of automation. And if that is a legit threat in your model, you are going to have a bad time.
It’s just going to trip you up at some pointI’m not saying it should be your only defense. I’m saying that changing defaults is a good idea for secure systems.
For instance, you should change the default WiFi password on your router.
Yes, because a password is security
But scriptkiddies and automated scans are not a security threat. If they were a legitimate threat to your server, you have bigger problems.
All it does is reduce log chatter.Anyone actually wanting in would port scan, then try and connect to each port, and quickly identify an SSH port
Imagine that the xz exploit actually made it into your server, so your sshd was vulnerable. Having it on another port does seem helpful then. In fact i sometimes think of putting mine on a random secret address in the middle of a /64 ipv6 range, but I haven’t done that yet.
it occurs to me, the xz exploit and similar is a good reason not to run the latest software. It affected Debian Sid but not the stable releases. I’m glad I only run the stable ones.
Imagine that the xz exploit actually made it into your server, so your sshd was vulnerable. Having it on another port does seem helpful then.
Nope. Your entire server can be scanned in less than a second for an open ssh port.
IPv6 does not change the fact since when your server is attacked the hist IP is already known.
Don’t turn it on is the ultimate technique
That’s why “availability” is a core tenet of security (according to some cybersecurity course I took). It is easy to prevent unauthorized access to data if you have no requirements on authorized access.
barring that, unplug the ethernet.
Use a hardened-by-default OS like OpenBSD, HardenedBSD, or something similar in Linux.
Setup Fail2ban
Login only with SSH keys. MFA on SSH login. Use SSH proto 2.
Disable passwords, x11 forwarding, root logins
Reduce Idle timeout interval
Limit users’ SSH access
That should be more than enough for the average use case.
You can have 2FA on ssh?
Yep. Use SSH keys, not just protocol.
On connection, it’ll ask for your SSH password (this is different from the users password).
After that with something like authelia in place, you’ll be asked for a 2fa code.
So, no. SSH can’t do 2FA? I would need to set up Authelia and connect through that? I already use ssh keys instead of passwords to connect to my server
Yes it can. I literally have it set up right now.
When I connect to my vps I am promoted for the password for my SSH key. Only works on a machine that has the ssh key.
Then I need to use 2fa.
Ah, so it the asks for the TOTP provided by Authelia? I misunderstood, sorry. That’s pretty cool. Do you maybe still have the guide you used to set that up?
It is possible to have 2FA with a security key and ssh. Been on my to do list for some time to try it.
Regular updates are definitely necessary too. Also, if you do limit SSH users to a chroot make sure you limit TCP (port) forwarding too.
- crowdsec
- SSH - change port, disable root login, disable password login, setup SSH keys using SK(YubiKey in my case)
- nftables - I use https://github.com/etkaar/nftm to keep things quick and simple. I like the fact if will convert DNS entries to IPs. I then just use dynamic DNS update clients on all my endpoints
- WireGuard for access to services other than SSH(in some cases port 443 will be open if its a web server or proxy)
- rsyslog to forward auth logs to my central syslog server
disable root login
That does not do much in practice. When a user is compromised a simple alias put in the .bashrc can compromise the sudo password.
Explicitly limit the user accounts that can login so that accidentally no test or service account with temporary credentials can login via ssh is the better recommendation.
I think the point is that root is a universal user found on all linux systems where as users have all kinds of names. It narrows down the variables to brute-force, so simply removing the ability to use it means they have to guess a username and a password.
guess a username and a password.
Security by obscurity is no security. Use something like fail2ban to prevent brute force. When you use a secure password and or key this also does not matter much.
Something something don’t let ‘good’ be the enemy of ‘perfect’
Kicksecure Debian CLI: https://www.kicksecure.com/wiki/Debian
Air gapping
/s
Ubuntu has a set of scripts you can run to harden a new server (not advisable on a server that has already been configured for something). You need an Ubuntu Pro subscription to access them but you can get a free trial and then cancel it after you’ve finished.
More info at https://ubuntu.com/security/cis.
I did this process for a customer recently and it was pretty straightforward and much much more thorough (over 100 configuration changes) than just tweaking SSH and fail2ban.
I expect other commercially-oriented distros offer something similar.
Fwiw you don’t need to cancel or trial anything. Everyone can get free Ubuntu pro licensesbfor up to 5 machines
