Thursday, November 12, 2015

IPs hammering Postfix

So, I've been lax in checking my logs lately, but decided to check them last night on my Linode server, which is running Ubuntu.

I'm running PSAD but for some reason, it stopped reporting scanning IPs to me. I've fixed that but it won't account for the last few months of PSAD not working.

What I'm seeing in the syslogs are connection attempts to my Postfix mail server. The server appears to have automatically dropped the traffic. I see no indication that Iptables tried to block the traffic, but this is probably due to needing to have Postfix open to the internet.

I can either rely on Postfix to continue to kill these connection attempts or I can add them to the firewall. First, I've to compile a listing of unique IPs (there were many duplicates as well as other connection information that needed to be removed).

The first thing I did was filter any logs not relevant to Postfix and redirect that output to a file. In fact what I did was grep the syslogs using the following filter: 'disconnect from unknown', which showed me every instance of Postfix disconnecting an IP from communication:



root@linode:/var/log# grep 'disconnect from unknown' syslog > /root/postfix_drops

Nov 12 05:44:12 linode postfix/smtpd[15130]: disconnect from unknown[198.206.134.152]
Nov 12 05:46:10 linode postfix/smtpd[15176]: disconnect from unknown[203.157.41.130]
Nov 12 05:57:11 linode postfix/smtpd[15366]: disconnect from unknown[91.205.167.98]
Nov 12 06:03:48 linode postfix/smtpd[15424]: disconnect from unknown[198.206.134.152]
Nov 12 06:05:49 linode postfix/smtpd[15467]: disconnect from unknown[155.208.242.236]
Nov 12 06:17:03 linode postfix/smtpd[15677]: disconnect from unknown[203.122.41.195]
Nov 12 06:17:20 linode postfix/smtpd[15677]: disconnect from unknown[112.175.103.29]
Nov 12 06:21:59 linode postfix/smtpd[15861]: disconnect from unknown[122.154.46.172]
Nov 12 06:22:20 linode postfix/smtpd[15861]: disconnect from unknown[155.208.242.236]
Nov 12 06:23:41 linode postfix/smtpd[15861]: disconnect from unknown[198.206.134.152]
Nov 12 06:35:21 linode postfix/smtpd[16335]: disconnect from unknown[122.154.46.172]
Nov 12 06:48:00 linode postfix/smtpd[16516]: disconnect from unknown[203.157.41.130]


The small snippet above shows that there are repeat offenders.  That'll need to be sorted out but we'll do that later.  Right now, all I need are the IPs.  I've to remove everything else.

I then use the following to remove a good bit of the logs:



root@linode:/var/log# nawk '{print $8}' /root/postfix_drops > /root/postfix_drops_2

The result is:


unknown[91.205.167.98]
unknown[198.206.134.152]
unknown[155.208.242.236]
unknown[203.122.41.195]
unknown[112.175.103.29]
unknown[122.154.46.172]
unknown[155.208.242.236]
unknown[198.206.134.152]
unknown[122.154.46.172]
unknown[203.157.41.130]

Note that everytime I'm making a change to the output, I'm also redirecting the output to a new file.

I then remove all instances of 'unknown' from the file (I had to add spaces between the the pointed brackets and the word "unknown", otherwise neither will render...remove the spaced for the code to work properly):

root@linode:/var/log# sed 's/\< unknown \>//g' /root/postfix_drops_2 > /root/postfix_drops_3

[155.208.242.236]
[203.122.41.195]
[112.175.103.29]
[122.154.46.172]
[155.208.242.236]
[198.206.134.152]
[122.154.46.172]
[203.157.41.130]

All that's left are removing the brackets:

root@linode:/var/log# sed 's/\[//g;s/\]//g' /root/postfix_drops_3 > /root/postfix_drops_4
203.122.41.195
112.175.103.29
122.154.46.172
155.208.242.236
198.206.134.152
122.154.46.172
203.157.41.130



I then sort the file while also only wanting to see unique IPs:


root@linode:/var/log# sort -u /root/postfix_drops_4
94.156.37.145
94.156.37.146
94.156.37.147
94.156.37.148
94.156.37.149
94.156.37.150

I started out with 394 lines and ended up with 94 unique IPs, across two syslog files.  I still have to do the archived syslog files.  I also saw that the 94 IPs show many IPs that are in sequence, which means that the culprits are trying to distribute the attacks over a range of IPs (I've posted similar attacks when analyzing SSH logs).

The resulting log file is here.

So, now, I can either be happy with how Postfix is handling the traffic or add the IPs to my firewall ruleset.  This was more of an exercise in seeing how well I could quickly assess the nature of the traffic in question and I'm happy (it was simple enough, although I'm out of practice in doing such things).

UPDATE:

1. I scrubbed the archived syslog files and the total, including those IPs I already scrubbed, is 959, and when sorted uniquely, there are 301 IPs.

2.  I added the first batch of IPs to /etc/hosts.deny for tcpwrappers to block.  I also found that I couldn't use tcpwrappers since I didn't compile postfix with tcpwrapper support, so I installed xinetd (which can wrap services inside itself with some configuration).  I'll monitor to see if the IPs will be blocked and if it doesn't work, I'll add the IPs to the firewall's ruleset.
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