Hi,
I know this is quite impossible to diagnose from afar, but I came across the posting from lemmy.world admins talking about the attacks they are facing where the database will get overwhelmed and the server doesn’t respond anymore. And something similar seemed to have happened to my own servers.
Now, I’m running my own self-hosted Lemmy and Mastodon instances (on 2 seperate VPS) and had them become completely unresponsive yesterday. Mastodon and Lemmy both showed the “there is an internal/database error” message and my other services (Nextcloud and Synapse) didn’t load or respond.
Login into my VPS console showed me that both servers ran at 100% CPU load since a couple of hours. I can’t currently SSH into these servers, as I’m away for a couple of days and forgot to bring my private SSH key on my Laptop. So, for now I just switched the servers off.
Anyway, the main question is: what should I look at in troubleshooting when I’m back home? I’m a beginner in selfhosting and I run these instances just for myself and don’t mind if I’d have to roll them back a couple days (I have backups). But I would like to learn from this and get better at running my own services.
For reference: I run everything in docker containers behind Nginx Proxy Manager as my reverse proxy. I have only ports 80, 443 and 22 open to the outside. I have fail2ban set up. The Mastodon and Lemmy instances are not open for registration and just have 2 users each (admin + my account).
I run a lemmy server. If you ban a bot and remove content (even if the bot is from another instance), if you’re removing more than a few comments the think will lock up, the server will error, and you’ll pretty much have to restart it. This could also cause other services to be unresponsive as the CPU will be sitting at 100% for the thread.
If you think it’s genuinely a DDOS (which is unlikely if you’re a small fry, but possible), then try putting cloudflare in front of your service (it’s free) which will mitigate many types of DOS attacks.
I can’t help much regarding the service denial issue.
However Port 22 should never be open to the outside world. Limiting to key authentication is a really good first step.
To avoid automated scans you should also change the port to a higher number, maybe something above 10,000.
This both saves traffic and CPU. And if a security bug in sshd exists this helps, too.
However Port 22 should never be open to the outside world.
Wat. How do you connect with ssh, then? You can bind openssh to an other port, but the only thing it changes is that you have less noise in your logs. The real most important security measure is to make sure your softwares are always up to date, as old vulnerable software is the first cause of penetration (and yes, it’s better to deactivate password login to only use ssh keys).
As long as you do not allow password logins for ssh you can let the silly idiots beat their heads against it or you could use a script to ban them. They will not brute force a properly secured ssh server.
I would be mostly annoyed about the log entries. That would be my primary motivation to ban script kiddy hack attempts.
One could setup a VPN and expose the SSH port to the VPN network only. It think tailscale operates this way?
I’m not sure about the feasibility of this (my first thought would be that ssh on the host can be accessed directly by IP, unless maybe the VPN software creates its own network interface and sshd binds on it?), but this does not remove the need for frequent updates anyway, as openssh is not the only software that could have bugs : every software that opens a port should be protected as well, and you can’t hide your webserver on port 80 behind a VPN if you want it to be public. And it’s anyway a way more complicated setup than just doing updates weekly. :)
The points I made should not be used instead of all other security precautions like prohibited password login, fail2ban and updates, I thought that is common knowledge. It’s additional steps to increase security.
I disagree that changing the port is just security by obscurity. Scanning ips on port 22 is a lot easier than probing thousands of ports for every IP.
The reason people do automated exploit attempts on port 22 is because it is fast, cheap and effective. By changing the port you avoid these automated scans. I agree with you, this does not help if someone knows your IP and is targeting you specifically. But if you’re such a valuable target you hopefully have specialized people protecting your IT infrastructure.
Edit: as soon as your sshd answers on port 22, a potential attacker knows that the IP is currently in use and might try to penetrate. As stated above, this information would most likely not be shared with the automated attacks if you used any random port.
If you do not neglect updates, then by all mean, changing ports does not hurt. :) Sorry if I may have strong reaction on that, but I’ve seen way too many people in the past couple decades counting on such anecdotal measures and not doing the obvious. I’ve seen companies doing that. I’ve seen one changing ports, forcing us to use the company certificate to log in, and then not update their servers in 6 months. I’ve seen sysadmins who considered that rotating servers every year made it useless to update them, but employees should all use Jumpcloud “for security reasons”! Beware, though, mentioning port changing without saying it’s anecdotal and the most important thing is updates, because it will encourage such behaviors. I think the reason is because changing ports sounds cool and smart, while updates just sound boring.
That being said, port scanning is not just about targeted pentesting. You can’t just run nmap on a host anymore, because IDS (intrusion detection systems) will detect it, but nowadays automated pentesting tools do distributed port scanning to bypass them : instead of flooding a host to test all their ports, they test a range of hosts for the same port, then start over with a new port. It’s half-way classic port scanning and the “let’s just test the whole IP range for a single vulnerability” that we more commonly see nowadays. But they are way harder to detect, as they scan smaller sets of hosts, and there can be hours before the same host is tested twice.
To avoid automated scans you should also change the port to a higher number, maybe something above 10,000.
This doesn’t really work any more. Port scanning is trivial with IPv4, and tools like masscan can scan the entire IPv4 internet (all IPv4 addresses) in less than 15 minutes.
Very interesting, thanks for sharing!
I know it’s just anecdotal evidence, however fail2ban in my one machine which does need ssh on port 22 to the open internet bans a lot of IPs every hour. All other ones with ssh on a higher port do not. Also their auth log does not show any failed attempts.
The best you can do to know if it was an attack is to inspect the logs when you have time. There are a lot of things that can cause a process going wild without being an attack. Sometimes, even filling the RAM can cause the CPU to appear overloaded (and will freeze the system anyway). One simple way to figure out if it’s an attack : reboot. If it’s a bug, everything will get back to normal. If it’s a DDoS, the problem will reappear up to a few minutes after reboot. If it’s a simple DoS (someone exploiting a bug of a software to overload it), it will reappear or not given if the exploit was automated and recurring, or was just a one-shot.
The fact that both your machines fell at the same time would tend to make think it’s an attack. On the other hand, it may just be a surge of activity on the network with VPSes with way not enough resources to handle it. Or it may even be a noisy neighbor problem (the other people sharing with you the real hardware on which your VPSes run who will orverload it).
Lemmy has the disadvantage of being opensource. In the long run this can be good for security but in the short term this gives your enemies a blueprint of your software and they know exactly how to attack you.
The only time I have every been compromised was when I was running 3rd party code open to the internet. I have been running my own code open to the internet for 20+ years and have been safe with it. I don’t think I am some kind of god coder or anything but I am mindful of best practices and most importantly I am a small fish in a big pond.
Long story short is that running popular 3rd party code open to the internet exposes you to unique threats that you should be prepared for. Subnet/vlan it, vpn it, lock it down,
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 |
| UDP | User Datagram Protocol, for real-time communications |
| VPN | Virtual Private Network |
| VPS | Virtual Private Server (opposed to shared hosting) |
6 acronyms in this thread; the most compressed thread commented on today has 9 acronyms.
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