Re: SSH server under attack...

[Matt Alexander <lowbassman () gmail com>]

Calm down...  People are always going to try to hack your box.  Just do 
as much as you can to prevent them from getting anywhere.

First, make sure your password is not something that can be cracked from 
a dictionary attack.

Second, configure SSH to only allow certain users by adding the 
following line to your sshd_config:

    AllowUsers dave

Third, block the attacker:

    iptables -A INPUT -s 200.55.192.29 -j DROP

You might also consider running SSH on a much higher port that nmap and 
other port scanners don't check by default.

It wouldn't be too difficult to write a shell script that watches your 
logs for repeated login failures and then automatically blocks the 
attacker with iptables.  Make sure the script doesn't allow iptables to 
block the IP's you regularly login from, of course.

If you want to get carried away, you could setup Port Knocking using 
iptables or one of the other many PK progs out there.
~M


Dave wrote:
> My SSH server has been under DoS and I cant stop it!!!
>
> I changed the port of the SSH server from 22 to 2222. This isnt going to
> really do much but it would stop some automated script that attacks port
> 22. OK...within a few hours the server was being attacked again on port
> 2222. This is an *active* attacker, active in that he is actively
> monitoring what he is doing. The router/firewall logs dont show any
> dropped packets sent to port 22 so he changed the port of the attack
> script. Now, the new machine to attack me is 200.55.192.29. This belongs
> to a company in south america called 'Springs South America Textiles
> Ltda.'. I scanned the machine and found that it is hosting a webserver
> (Apache/2.0.52 (Fedora) Server at www.springs.cl) among other services.
> The last machine the attacker used to brute_force me was also an apache
> server (rh linux). So this attacker is cracking various webservers (most
> likely) or some other service on these boxes in order to use these
> machines as an attack platform. Now, yes, i notified the admin of this
> company etc..but think of this. If this admin is going to put an
> *unused* and unprotected server on the net then what kind of admin is
> he? Will he even care about my email? Who knows! Calling the authorities
> is not going to work 'cause frankly I am a nobody...who cares if my
> servers are under attack! No one is going to waste resource (money) in
> trying to find this guy, so really its up to me. So what do we know
> about this guy? At first the info seems conflicting: He has the ability
> to crack a number of random servers and use them at his disposal but he
> is running the same stupid attack over and over...why? First off, the
> attack is a brute force attack. He is trying to guess a username
> password combo in order to be able to log into my server and get shell
> access...but maybe not. Like I said..he is no dummy. So what is he
> doing? I think DoS (denial of service) , the brute force tool is just
> the means to an end. He isnt trying to break in by doing this. Maybe he
> coudnt break in to my server so he is resorting to the next trick up his
> sleeve. By having all these machines attempting to log into my server
> over and over he might be trying to use up my bandwidth in effect
> causing a DoS to anyone! OR...In closely looking at the logs you will
> notice something *unusual*:
>
> Failed password for invalid user admin from ::ffff:200.55.192.29 port
> 34182 ssh2
> Invalid user admin from ::ffff:200.55.192.29
> Failed password for invalid user admin from ::ffff:200.55.192.29 port
> 34679 ssh2
> Invalid user admin from ::ffff:200.55.192.29
> Failed password for invalid user admin from ::ffff:200.55.192.29 port
> 34752 ssh2
> Invalid user administrator from ::ffff:200.55.192.29
> Failed password for invalid user administrator from ::ffff:200.55.192.29
> port 35253 ssh2
> Invalid user administrator from ::ffff:200.55.192.29
> Failed password for invalid user administrator from ::ffff:200.55.192.29
> port 35735 ssh2
> Invalid user administrator from ::ffff:200.55.192.29
> Failed password for invalid user administrator from ::ffff:200.55.192.29
> port 36237 ssh2
> Invalid user tads from ::ffff:200.55.192.29
> Failed password for invalid user tads from ::ffff:200.55.192.29 port
> 36703 ssh2
> Invalid user tads from ::ffff:200.55.192.29
> Failed password for invalid user tads from ::ffff:200.55.192.29 port
> 36813 ssh2
> Invalid user tads from ::ffff:200.55.192.29
> Failed password for invalid user tads from ::ffff:200.55.192.29 port
> 37332 ssh2
> Invalid user tip from ::ffff:200.55.192.29
> Failed password for invalid user tip from ::ffff:200.55.192.29 port
> 37820 ssh2
> Invalid user tip from ::ffff:200.55.192.29
> Failed password for invalid user tip from ::ffff:200.55.192.29 port
> 38267 ssh2
> Invalid user tip from ::ffff:200.55.192.29
> Failed password for invalid user tip from ::ffff:200.55.192.29 port
> 38757 ssh2
> Invalid user myra from ::ffff:200.55.192.29
> Failed password for invalid user myra from ::ffff:200.55.192.29 port
> 38844 ssh2
> Invalid user myra from ::ffff:200.55.192.29
> Failed password for invalid user myra from ::ffff:200.55.192.29 port
> 39333 ssh2
> Invalid user myra from ::ffff:200.55.192.29
> Failed password for invalid user myra from ::ffff:200.55.192.29 port
> 39812 ssh2
> Invalid user jack from ::ffff:200.55.192.29
> Failed password for invalid user jack from ::ffff:200.55.192.29 port
> 40312 ssh2
> Invalid user jack from ::ffff:200.55.192.29
> Failed password for invalid user jack from ::ffff:200.55.192.29 port
> 40787 ssh2
> Invalid user jack from ::ffff:200.55.192.29
> Failed password for invalid user jack from ::ffff:200.55.192.29 port
> 40893 ssh2
> Invalid user sya from ::ffff:200.55.192.29
>
>
> Each user name was tried three times. What does this
> mean...I dont know but right off hand I would guess that he is trying to
> lock out legit user accounts. You see some servers will disallow a user
> to log in if they entered three wrong passwords. This, strangely enough,
> is used to help stop brute forcing!!! Anyway, The attacker has put
> together a list of *potential* user names that *might* be found on my
> server and is attempting to lock them out...in effect creating a DoS to
> any users whose names appear on this list.
>
> He also knew right away when I changed the sshd port number and wasted
> no time in getting another machine to attack me via this port!
>
> Authorities arent going to help...Servers admin prob doesnt care plus
> the attacker most likely has access to any number of servers so writing
> the abuse lines could be a daily chore just to keep up...any
> recommendations?
>
> Any help / comments / flames appreciated
>
> take it easy...
> dave
>
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