Tuesday, November 24, 2015

IPTables and SSH - Resetting Brute Force Traffic, UPDATE

I showed how to determine IPs that were bruteforcing in my last blog entry, and how to block the majority of it (the posts are here and here).

In checking my logs over the last week, I see some activity that's making it through the firewall.  To be honest, I doubt I'll be able to filter ALL the bruteforcing using the rules I've currently in place.  I did tweak them a bit, changing the 4th and 5th rules' threshold to 60 seconds (vs 30 seconds).  It helped some but then I saw one particular IP blast through the firewall's ruleset like it was designed to go low and slow.

Here are the IPs that have been bruteforcing port 22 this week, as well as their hit counts:
root@linode:~/ssh_brute_force_logs# sed 's/S.*=//' combined1 | uniq -c
      2 183.60.48.25
      2 162.13.76.111
      2 183.60.48.25
      2 113.108.21.16
   1334 221.231.139.206
      2 183.60.48.25
      1 217.91.114.240
      2 113.108.21.16
      2 207.46.140.7
      1 218.4.117.26
      2 113.108.21.16
      8 146.88.41.119
      2 113.108.21.16
      1 218.60.99.51
      2 113.108.21.16
      1 187.120.217.121
      1 113.108.21.16
      1 43.229.53.49
      2 113.108.21.16
      2 43.229.53.49
      6 61.146.150.209
      1 94.23.60.117
      5 61.146.150.209
      2 113.108.21.16
      1 179.48.253.43
      2 51.254.137.164
      1 104.20.64.58
      1 51.254.137.164
      1 178.187.137.68
      2 113.108.21.16
     39 140.115.36.207
      2 113.108.21.16
      3 119.90.18.7
      2 113.108.21.16
      1 121.43.169.81
      1 113.108.21.16
      1 203.129.217.5
      1 113.108.21.16
      1 106.57.172.14
      2 14.160.13.174
      2 113.108.21.16
      2 119.90.18.7
IP 221.231.139.206 was the most prevalent by far, with IP 140.115.36.207 coming in second.

I'm to the point where I should create a script that would determine any IP with a hit count of, for example, 1000, and block them.  Or I can just use opensource products like fail2ban (remember, denyhosts isn't working because tcpwrapper support isn't compiled into inetd.conf on Ubuntu 14.04 LTS.).  So, I've installed fail2ban and will watch to see how it blocks things with the default setting before making changes to the configuration.  The cool thing about fail2ban is that it will watch and block more than just SSH activity.

Am I worrying too much about this?  Some would say, YES!  I'm doing this for learning purposes and also to get a better understanding of how such bruteforcing is evolving, but I don't really want to have to deal with a box that has been hacked, either.  Every admin has the responsiblity of doing their utmost to ensure their machines aren't hacked...that means that the admin needs to be proactive in placing defenses to deter or slow down attacks.

UPDATE:

Already, I see the following in the fail2ban logs:

2015-11-24 22:33:10,453 fail2ban.actions: WARNING [ssh] Ban 195.154.46.203
2015-11-24 22:33:10,458 fail2ban.actions: WARNING [ssh] Ban 59.47.0.157
2015-11-24 22:33:10,462 fail2ban.actions: WARNING [ssh] Ban 43.229.53.49
2015-11-24 22:33:10,466 fail2ban.actions: WARNING [ssh] Ban 43.229.53.87
2015-11-24 22:43:11,085 fail2ban.actions: WARNING [ssh] Unban 195.154.46.203
2015-11-24 22:43:11,090 fail2ban.actions: WARNING [ssh] Unban 59.47.0.157
2015-11-24 22:43:11,094 fail2ban.actions: WARNING [ssh] Unban 43.229.53.49
2015-11-24 22:43:11,098 fail2ban.actions: WARNING [ssh] Unban 43.229.53.87

Fail2ban banned and then unbanned the IPs 10 minutes later (default settings).

What I need to study is how Fail2ban is implementing the bans.  Also, do I want to outright permanently ban these IPs...is that even feasible?  We'll see.

UPDATE 2 - 12/24/2016:

I checked on things.  I checked today's bans since I've been out of touch with the server and Linux in general (been doing work-related things but nothing close to this type of stuff).  I didn't even remember how log Fail2ban was blocking but I see I changed the default from 10 minutes to 7 days.  I was too lazy to check the logs, so what I did was pick an IP from the ban logs and grep for it.  I saw it banned and saw it unbanned 7 days later.

The logs go as far back as 11/20.  The trend seems to be mid teens for Nov, although I saw several spikes to the mid twenties.  I'm just checking to see what the norm is, so that as I begin to get back into the swing of things, I have a baseline to compare.  It would be nice if I could archive these files somehow.

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