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.
this post was submitted on 20 Apr 2024
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Regular updates are definitely necessary too. Also, if you do limit SSH users to a chroot make sure you limit TCP (port) forwarding too.
Containers can help lock services down if you do it right.
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.
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(4 replies)
- 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"
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.
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.
- 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'
Check out online resources such as the Nist cyber stuff.
Basic things include disabling unnecessary services, disabling password authentication, setting up and verifying the firewall, configuring selinux and so on.
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.
Firewall and deciding on an entry point for system administration is a big consideration.
Generating a strong unique password helps immensely. A password manager can help with this.
If this is hosting services reducing open ports with something like Nginx Proxy Manager or equivalent. Tailscale and equivalent(wire guard, wireguard-easy, headscale, net bird, and net maker) are also options.
Getting https right. It's not such a big deal if all the services are internal. However, it's not hard to create an internal certificate authority and create certs for services.
If you have server on a VPS. Firewall is again your primary defense. However, if you expose something like ssh fail2ban can help ban ips that make repeated attempts to login to your system. This isn't some drop in replacement for proper ssh configuration. You should be using key login and secure your ssh configuration away from password logins.
It also helps if you are using something like a proxy for services to setup a filter list. NPM for example allows you to outright deny connection attempts from specific IP ranges. Or just deny everything and allow specific public IPs.
Also, if you are using something like proxmox. Remember to configure your services for least privileges. Basically the idea being just giving a service what it needs to operate and no more. This can encompass service user/group names for file access ect.
All these steps add up to pretty good security if you constantly assess.
Even basic steps in here like turning on the firewall and only opening ports your services need help immensely.
The biggest thing is to change the defaults and to limit access. Unless your are the target of a nation state the attacks against your network will be automated.
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.
Minimize installation and keep it streamlined. Update promptly. Choose applications that are still supported or have an active community.
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.
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| DNS | Domain Name Service/System |
| IP | Internet Protocol |
| SSH | Secure Shell for remote terminal access |
| SSL | Secure Sockets Layer, for transparent encryption |
| TCP | Transmission Control Protocol, most often over IP |
| VNC | Virtual Network Computing for remote desktop access |
| VPN | Virtual Private Network |
| VPS | Virtual Private Server (opposed to shared hosting) |
[Thread #693 for this sub, first seen 20th Apr 2024, 15:55] [FAQ] [Full list] [Contact] [Source code]
Stumbled uppon this guide
https://github.com/imthenachoman/How-To-Secure-A-Linux-Server
I think its a good place to start
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.
Leak the scripts?
Fwiw you don't need to cancel or trial anything. Everyone can get free Ubuntu pro licensesbfor up to 5 machines
Run SCAP tool with a STIG baseline.
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