Recently, I discovered that SSH of my VPS server is constantly battered as follows.
Apr 06 11:15:14 abastro-personal-arm sshd[102702]: Unable to negotiate with 218.92.0.201 port 53768: no matching key exchange method found. Their offer: diffie>
Apr 06 11:30:29 abastro-personal-arm sshd[102786]: Unable to negotiate with 218.92.0.207 port 18464: no matching key exchange method found. Their offer: diffie>
Apr 06 11:45:36 abastro-personal-arm sshd[102881]: Unable to negotiate with 218.92.0.209 port 59634: no matching key exchange method found. Their offer: diffie>
Apr 06 12:01:02 abastro-personal-arm sshd[103019]: Unable to negotiate with 218.92.0.203 port 16976: no matching key exchange method found. Their offer: diffie>
Apr 06 12:05:49 abastro-personal-arm sshd[103066]: Unable to negotiate with 218.92.0.212 port 49130: no matching key exchange method found. Their offer: diffie>
Apr 06 12:07:09 abastro-personal-arm sshd[103077]: Connection closed by 162.142.125.122 port 56110 [preauth]
Apr 06 12:12:18 abastro-personal-arm sshd[103154]: Connection closed by 45.79.181.223 port 22064 [preauth]
Apr 06 12:12:19 abastro-personal-arm sshd[103156]: Connection closed by 45.79.181.223 port 22078 [preauth]
Apr 06 12:12:20 abastro-personal-arm sshd[103158]: Connection closed by 45.79.181.223 port 22112 [preauth]
Apr 06 12:21:26 abastro-personal-arm sshd[103253]: Connection closed by 118.25.174.89 port 36334 [preauth]
Apr 06 12:23:39 abastro-personal-arm sshd[103282]: Unable to negotiate with 218.92.0.252 port 59622: no matching key exchange method found. Their offer: diffie>
Apr 06 12:26:38 abastro-personal-arm sshd[103312]: Connection closed by 92.118.39.73 port 44400
Apr 06 12:32:22 abastro-personal-arm sshd[103373]: Unable to negotiate with 218.92.0.203 port 57092: no matching key exchange method found. Their offer: diffie>
Apr 06 12:49:48 abastro-personal-arm sshd[103556]: error: maximum authentication attempts exceeded for root from 98.22.89.155 port 53675 ssh2 [preauth]
Apr 06 12:49:48 abastro-personal-arm sshd[103556]: Disconnecting authenticating user root 98.22.89.155 port 53675: Too many authentication failures [preauth]
Apr 06 12:49:51 abastro-personal-arm sshd[103558]: error: maximum authentication attempts exceeded for root from 98.22.89.155 port 53775 ssh2 [preauth]
Apr 06 12:49:51 abastro-personal-arm sshd[103558]: Disconnecting authenticating user root 98.22.89.155 port 53775: Too many authentication failures [preauth]
Apr 06 12:49:53 abastro-personal-arm sshd[103561]: error: maximum authentication attempts exceeded for root from 98.22.89.155 port 53829 ssh2 [preauth]
Apr 06 12:49:53 abastro-personal-arm sshd[103561]: Disconnecting authenticating user root 98.22.89.155 port 53829: Too many authentication failures [preauth]
Apr 06 12:49:54 abastro-personal-arm sshd[103563]: Connection closed by 98.22.89.155 port 53862 [preauth]
Apr 06 12:50:41 abastro-personal-arm sshd[103576]: Invalid user from 75.12.134.50 port 36312
Apr 06 12:54:26 abastro-personal-arm sshd[103621]: Connection closed by 165.140.237.71 port 54236
Apr 06 13:01:26 abastro-personal-arm sshd[103702]: Connection closed by 193.32.162.132 port 33380
Apr 06 13:03:40 abastro-personal-arm sshd[103724]: Unable to negotiate with 218.92.0.204 port 60446: no matching key exchange method found. Their offer: diffie>
Apr 06 13:11:49 abastro-personal-arm sshd[103815]: Received disconnect from 165.140.237.71 port 50952:11: [preauth]
Apr 06 13:11:49 abastro-personal-arm sshd[103815]: Disconnected from authenticating user root 165.140.237.71 port 50952 [preauth]
Apr 06 13:19:08 abastro-personal-arm sshd[103897]: Unable to negotiate with 218.92.0.208 port 59274: no matching key exchange method found. Their offer: diffie>
Apr 06 13:33:36 abastro-personal-arm sshd[104066]: Received disconnect from 165.140.237.71 port 50738:11: [preauth]
Apr 06 13:33:36 abastro-personal-arm sshd[104066]: Disconnected from authenticating user ubuntu 165.140.237.71 port 50738 [preauth]
Apr 06 13:34:50 abastro-personal-arm sshd[104079]: Unable to negotiate with 218.92.0.204 port 44816: no matching key exchange method found. Their offer: diffie>
Apr 06 13:50:32 abastro-personal-arm sshd[104249]: Unable to negotiate with 218.92.0.206 port 27286: no matching key exchange method found. Their offer: diffie>
Apr 06 13:51:58 abastro-personal-arm sshd[104261]: Received disconnect from 165.140.237.71 port 50528:11: [preauth]
Apr 06 13:51:58 abastro-personal-arm sshd[104261]: Disconnected from authenticating user root 165.140.237.71 port 50528 [preauth]
Apr 06 14:01:25 abastro-personal-arm sshd[104351]: Invalid user from 65.49.1.29 port 18519
Apr 06 14:01:28 abastro-personal-arm sshd[104351]: Connection closed by invalid user 65.49.1.29 port 18519 [preauth]
As you can see, it is happening quite frequently, and I am worried one might break in at some point. Since SSH access guards users with root-access, it can be quite serious once penetrated. How do I harden against these kind of attacks? Because this is VPS, disabling SSH is a no-go (SSH is my only entry of access). Are there ways to stop some of these attackers?
As always, thanks in advance!
About the best you can do.
Don’t reject connections to port 22, honeypot it and ban on connection attempt.
I’d get myself banned this way. I forget the -p flag at least once per week.
That’s a lot more work.
By all means, I am no expert, but isn’t it “just” the fail2ban?
Fail2ban blocks IPs that fail to connect repeatedly. A honeypot pretends fails worked and gives them a worthless environment to try to exploit. The purpose of fail2ban is to block attacks, the purpose of a honeypot is amusement and to waste attackers’ time.
I understood the comment as “leave the port open to ssh, to easily allow fail2ban to hit the ip’s before they get through your full port range.” But thanks for the elaborate answer :)
I agree, what you described is much more work ;)
Using a nonstandard port doesn’t get you much, especially popular nonstandard ports like 2222.
I used that port once and just as much junk traffic and ultimately regretted bothering.
Uhh… It gets you a lot. Specifically, unless you know the port you can’t connect… So hey, there’s that…
This community really says shit sometimes that makes me go cross-eyed…
The top-rated answer to this question on the Security StackExhange is “not really”. https://security.stackexchange.com/questions/189726/does-it-improve-security-to-use-obscure-port-numbers
On Serverfault, the top answer is that random SSH ports provide “no serious defense” https://serverfault.com/questions/316516/does-changing-default-port-number-actually-increase-security
Or the answer here, highlighting that scanners check a whole range ports and all the pitfalls of changing the port. Concluding: “Often times it is simply easier to just configure your firewall to only allow access to 22 from specific hosts, as opposed to the whole Internet.” https://security.stackexchange.com/questions/32308/should-i-change-the-default-ssh-port-on-linux-servers
And I’m a CEHv7. A literal security professional–and I say that an overwhelming vast majority of attacks against servers using SSH are going to come over the default port. Quite literally 99%. This means that you can lower your attack surface by exactly 99% by simply changing the default SSH port…
Those posts provide no meaningful insight and what they say is by the very technical of all interpretations is correct, I absolutely disagree with these statements. What they mean to say is that simply changing the default SSH port isn’t alone I means of strictly protecting yourself. Meaning you shouldn’t change the default SSH port and think that your server is secured because it’s not.
Quite the different interpretation than me saying it should be mandatorily a part of your security strategy.
In protecting yourself against port scanning is trivial.
Anyone underestimating the power of changing The default SSH port is someone who’s opinion I can safely disregard.
Do you have a source to cite for the literal 99%?
Reasoning skills and experience. There are entire botnets dedicated to finding servers with open SSH ports on 22. If the bots can connect, the IP of the server will be added to a list to be brute forced.
I’m a per diem linux systems administrator. Right now I have a VPS that I setup myself. It uses a non-standard ssh port, fail2ban, and rejects incoming connections to port 22. According to connection logs, I get about 200 attempts per 24 hours from bots randomly pinging ports to see if they can catch an open SSH port–and they’re banned via fail2ban.
I checked out some other servers that I manage, which I did not setup and have no control over how they operate. Sifting through just 3 random servers and checking connection logs, they have a combined 435,000 connection attempts in the past 6 hours between the 3 of them. These are relatively small servers with an extremely small presence. Simple fact of the matter is, is that they all have port 22 open and reachable. So botnets attempt to brute force them.
So just anecdotally that’s a difference of 0.0459770115% or 99.96%. Anyone telling you that changing the default SSH port doesn’t do anything for security has absolutely no practical experience at all. It significantly reduces your attack surface as bots have to guess at ports until they find your SSHd’s operational port to even begin to start sending attempts.
My experience running several ssh servers on uncommon nonstandard ports for over 10 years has been that it has eliminated all ssh brute forcing. I don’t even bother with fail2ban. I probably should though, just in case.
Also, PSA: if you use fail2ban, don’t try tab completing rsync commands without using
controlmasteror you will lock yourself out.My two cents: Using a nonstandard ssh port is good for dumping bots. True, you can easily do a port scan against a server and easily find all open ports nbd. But most off-the-shelf bots are looking for standard ports to penetrate. I know that when I format and reinstall the test server, as soon as I change the ssh port, bot noise goes down significantly. So, for a simple config edit and about 2 minutes of time, it seems worth the effort. It’s just one layer tho. And yes, it goes without saying to pick a port other than 22, 222, 2222, etc.
How about 22222?
Oh, that one’s fine. Everyone knows that 5-digit ports add extra security, which is why WireGuard runs on port 51820 by default. You can verify this by checking the max port number, which is also 5-digits, computers just aren’t powerful enough to crack 6-digit port numbers, so Linux hasn’t bothered increasing it. /s
It gets rid of most of the login attempts for me. I don’t use a popular port though. Pick a 5 digit port so they have to put in some effort to find it.