[stevendgarcia]

All of my VPS servers have been slammed in the last 5 days with bruteforce SSH attacks. I've never seen anything this aggressive. One of my servers got PWNed, which has never happened to me before. There's definitely some wild, shady shit going on.

[pfundstein]

I highly recommend installing fail2ban to automatically firewall IPs with consecutive failed attempts, or if possible, disable password authentication altogether and use key auth.

[stevendgarcia]

Solid advice. I had fail2ban installed and enabled. SSHD Root/password login turned off and only ssh key had access. My firewall was also airtight, or so I thought. Clearly I mucked up a config or setting somewhere because the odds of someone getting past all that are extremely low. One thing I had not prepared for was IP spoofing which I learned can be prevented with a few net.ipv4.conf tweaks. I also just purchased a static IP from my provider so I can lock down ssh access even further. Here's hoping I never have to deal with this headache again! fingers crossed

[xorcist]

You don't generally "get past" your firewall rules and into your box unless you have accounts that are not password protected.

If you really had password logins turned off, you need to identify and isolate how they gained access before you put that box online again. Never "hope" or "cross fingers" that it doesn't happen again. Unless you are an interesting target for some reason, chances are that these attacks are automated and you are running some insecure software somewhere.

Start by taking a snapshot of the machine before you do anything else. Go through the logs. Are there any unwanted processes? How were they started? Are there any unwanted binaries in the filesystem? How were they uploaded? Try to find IP addresses that that be tied to any unwanted login, and see search your logs for any previous occurrences.

Pay special attention to any web-reachable software you have installed.

[acegopher]

What was the vector by which they gained access? I have fail2ban, password login turned off, key access, airtight firewall, etc. and now am worried.

[steve19]

If they exploited a service or Web app they might have gotten shell access. The chance of gaining access through ssh with fail2ban is extremely unlikely, unless fail2ban was badly configured.

[cbluth]

Me too

[pfundstein]

How did you discover the breach, and did you determine the vector? My guess is that it was a pivoted breach from another system on the LAN such as your PC.

[stevendgarcia]

I'm still picking up the pieces but from my logs I can see that hundreds of successive login attempts were made from different IPs, effectively circumventing fail2ban with what I can only assume is some form of automated IP spoofing. I'm hoping that strict ipv4 settings and ssh ip range restrictions will mitigate this in the future. I also used this python script to harden my SSH security with better algorithms. https://github.com/arthepsy/ssh-audit

[nickphx]

No, you were not seeing spoofed traffic. There are that many compromised machines actively scanning.

[stevendgarcia]

It's scary to admit this but you are probably right. The first thing these bots do is use server resources to scan ports and brute force their way into other machines. I don't want to think about how many machines are pwned like this. Very sobering!

[OJFord]

> One thing I had not prepared for was IP spoofing which I learned can be prevented with a few net.ipv4.conf tweaks.

Do you have a handy link for more info about that?

`rp_filter`? https://www.slashroot.in/linux-kernel-rpfilter-settings-reve...

[ghostpepper]

Did you have password login disabled for all accounts or just the root account?

[avian]

+1 for disabling password auth. On the other hand I find fail2ban pretty useless these days. Most attacks I see seem to come from botnets where you only get a few requests from each IP.

[eridius]

I don't trust key-only auth; what if I need to access my machine from a new computer I haven't done this with before?

Is there any way to configure SSH to use a custom high-entry password that's different from the user's local password? My local password is something reasonable for me to type regularly (e.g. for sudo prompts), but I'd love to have a super long password just for SSH that I have to copy from my password manager each time.

[0lpbm]

If this is a scenario that happens often, you probably should invest in a portable method to hold your ssh keys, such as a smart card. I have only used YubiKey for this purpose, but I'm sure others, like the Nitrokey, work similarly.

[dahfizz]

This could be done simply by creating a new user with your super long password. Lock down ssh so you can only log in as this user, and let them `sudo su` into your normal working user.

[eridius]

I mean, yeah, but I don't want to do that. Partially because I don't want the friction, and partially because that won't work with any other tools that tunnel over ssh (e.g. sftp).

[eitland]

There will be friction, but sftp and port tunneling - which are my most used fwatures besides plain ssh - should be possible?

I mean either you sftp to a shared folder that can be accessed from your regular user as well or you use a staging area with a cron job (or you load/unload the staging area manually.)

[eridius]

If I'm sftp'ing to my server it's because I want to access my files. Not a special shared folder that I then have to separately ssh in, su to the real user, and move into place.

I'm not deploying a website so a staging area isn't applicable. This is just a VPS that I use for various purposes.

[ahje]

There are definitely cases where you might need to expose a an SSH setup where passwords are allowed to the World, but there is usually little reason to allow anyone to log in directly as root.

Set a long password for the user you log in as (correct horse battery staple-style passwords are perfect for such things), and make sure to put SSH on an alternate port to keep the more basic bots away and thereby reduce the noise.

Having to type a long password for sudo promts is a bit of a pain, but that trade-off is worth it from a security perspective.

[jmalicki]

"a custom high-entry password that's different from the user's local password?"

You mean an RSA private key? (no really, that's exactly what it is... you can put your private key in your password manager and copy it to your computer)

[eridius]

I can manually type in a 30-letter password that I can see from my password manager on my phone. I'm pretty sure I'm not going to be manually typing in an RSA private key stored on my phone.

[rorykoehler]

You can also setup a VPN and limit all port 22 activity to your VPNs IP.

[pbhjpbhj]

I know it's just an obscurity measure but step one is surely don't expose SSH on 22? Dropped my (home) attacks/scans to zero from hundreds per day.

[rorykoehler]

You could do that but if you become a target due to unexpected viral growth then it's useless.

[pbhjpbhj]

It's more "stops you appearing on Shodan" level. But surely if you can reduce the traffic then you are more likely to notice proper attacks.

[rorykoehler]

Shodan is amazing. Creepy too. I used to spend hours trawling video feeds on there. Fascinating.

[stevendgarcia]

Yep. I just paid my ISP for a static IP address to accomplish this exact thing.

[dharmab]

You should disable password auth entirely and whitelist the IPs you connect from in your firewall. If you need to conenct from a large range of possible IPs, use a bastion host with 2FA and restricted to IP blocks from countries you actually connect from.