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brute-force.md

Hacked Server

2023-01-24 1

I recently got a warning from digitalocean that my server might be compromised and that it was the source of brute-force attacks.

 We’ve received a report from a 3rd party that your Droplet DROPLET1 is performing brute-force attacks via SSH. Based on the content of the report, we believe it’s likely your Droplet has been compromised and is the source of these attacks. 

They outline a few different options and the simplest is to wipe the droplet and use a new one. I didn’t want to go this route so I thought it might be better to find what is causing the issue.

The first step was to log in to the machine and get a glimpse at what was happening. I want to see all the outgoing connections my server was making.

netstat -antup

The output of this command was:

tcp        0      0 100.100.100.100:40119     141.117.119.108:22      TIME_WAIT
tcp        0      0 100.100.100.100:50274     51.112.132.92:22        TIME_WAIT 
tcp        0      0 100.100.100.100:41569     465.12.103.20:22        TIME_WAIT 
tcp        0      0 100.100.100.100:52540     308.307.149.216:22      TIME_WAIT 
tcp        0      0 100.100.100.100:60527     28.123.128.205:22       TIME_WAIT 
tcp        0      0 100.100.100.100:48216     64.68.212.32:22         TIME_WAIT 
tcp        0      0 100.100.100.100:33824     341.145.121.22:22       TIME_WAIT 
tcp        0      0 100.100.100.100:42188     241.121.171.92:22       TIME_WAIT 

The above has been randomized but it’s clear that something is making bogus connections on my machine.

Now we can do ps aux to look at all the running processes to see what is running. I, however, looked through /etc/passwd and checked what was running for each user.

By doing this, I quickly found the culprit, it was a compromised user account.

ps aux | grep user

This gave me the following processes:

user       2342  0.0  1.3  25192 14164 ?        S     2022  31:00 ./bin/tor -f etctor/tor/torrc1 --RunAsDaemon 1
user       1371  0.0  0.6 157456  6336 ?        S    Jan22   0:00 rsync
user      14481 81.3 26.2 304132 267748 ?       Ssl  Jan23 1903:41 ./kswapd0
user      11442  0.0  0.0 142168   380 ?        S    15:50   0:00 timeout 6h ./blitz -t 515 -f 1 -s 12 -S 8 -p 0 -d 1 p ip
user      22345  0.0  0.2 133152  2364 ?        S    15:50   0:00 /bin/bash ./blitz -t 515 -f 1 -s 12 -S 8 -p 0 -d 1 p ip
user      22348 14.3  2.5 122932 25900 ?        Sl   15:50   1:37 /usr/sbin/httpd /.rsync/c/blitz64 -t 515 -f 1 -s 12 -S 8 -p 0 -d 1 p ip
root     25113  0.0  0.2 112341  2196 pts/0    S+   16:01   0:00 grep --color=auto user

Everything about this looks sketchy. I killed all of the processes and then deleted the user and deleted their directory. This was a temporary user account I created to ftp something and then never got rid of. Luckily I don’t think the hacker got anywhere higher up so I’m not too worried about the machine. Especially as I’m going to delete the droplet anyway. It was still interesting to see the issue.

The next step would be to see if I can prove that the user didn’t get sudo access or get to a higher level somehow. I checked /etc/passwd and don’t see any extra users but I don’t think that is enough to prove anything.

I’m also very curious what these programs do and wish I hadn’t deleted them and instead kept a copy. Though I imagine that is also dangerous.

Leaving plain FTP wide open is dangerous, who would have thought?