Blocking of international spam botnets with a Postfix plugin
This article contains an analysis and solution for blocking of international SPAM botnets and a tutorial to install the anti-spam plugin to postfix firewall - postfwd in the postfix MTA.
Introduction
One of the most important and hardest tasks for every company that provides mail services is staying out of the mail blacklists.
If a mail domain appears in one of the mail domain blacklists, other mail servers will stop accepting and relaying its e-mails. This will practically ban the domain from the majority of mail providers and prohibits that the provider’s customers can send e-mails. Tere is only one thing that a mail provider can do afterwards: ask the blacklist providers for removal from the list or change the IP addresses and domain names of its mail servers.
Getting into mail blacklist is very easy when a mail provider does not have a protection against spammers. Only one compromised customer mail account from which a hacker will start sending spam is needed to appear in a blacklist.
There are several ways of how hackers send spam from compromised mail accounts. In this article, I would like to show you how to completely mitigate international botnet spammers, who are characterized by logging into mail accounts from multiple IP addresses located in multiple countries worldwide.
How international botnet works
Hackers who use an international botnet for spamming operate very efficient and are not easy to track. I started to analyze the behaviour of such an international spam botnet in October of 2016 and implemented a plugin for postfix firewall - postfwd, which intelligently bans all spammers from international botnets.
The first step was the analysis of the behavior of an international spam botnet done by tracking of one compromised mail account. I created a simple bash one-liner to select sasl login IP addresses of the compromised mail account from the postfwd login mail logs.
Data in the following table are dumped 90 minutes after compromisation of one mail account and contains these attributes:
- IP addresses from which hacker logged into account (ip_address)
- Corresponding country codes of IP addresses from GeoIP database (state_code)
- Number of sasl logins which hacker did from one IP address (login_count)
+-----------------+------------+-------------+ | ip_address | state_code | login_count | +-----------------+------------+-------------+ | 41.63.176.___ | AO | 8 | | 200.80.227.___ | AR | 41 | | 120.146.134.___ | AU | 18 | | 79.132.239.___ | BE | 15 | | 184.149.27.___ | CA | 1 | | 24.37.20.___ | CA | 13 | | 70.28.77.___ | CA | 21 | | 70.25.65.___ | CA | 23 | | 72.38.177.___ | CA | 24 | | 174.114.121.___ | CA | 27 | | 206.248.139.___ | CA | 4 | | 64.179.221.___ | CA | 4 | | 184.151.178.___ | CA | 40 | | 24.37.22.___ | CA | 51 | | 209.250.146.___ | CA | 66 | | 209.197.185.___ | CA | 8 | | 47.48.223.___ | CA | 8 | | 70.25.41.___ | CA | 81 | | 184.71.9.___ | CA | 92 | | 84.226.27.___ | CH | 5 | | 59.37.9.___ | CN | 6 | | 181.143.131.___ | CO | 24 | | 186.64.177.___ | CR | 6 | | 77.104.244.___ | CZ | 1 | | 78.108.109.___ | CZ | 18 | | 185.19.1.___ | CZ | 58 | | 95.208.250.___ | DE | 1 | | 79.215.89.___ | DE | 15 | | 47.71.223.___ | DE | 23 | | 31.18.251.___ | DE | 27 | | 2.164.183.___ | DE | 32 | | 79.239.97.___ | DE | 32 | | 80.187.103.___ | DE | 54 | | 109.84.1.___ | DE | 6 | | 212.97.234.___ | DK | 49 | | 190.131.134.___ | EC | 42 | | 84.77.172.___ | ES | 1 | | 91.117.105.___ | ES | 10 | | 185.87.99.___ | ES | 14 | | 95.16.51.___ | ES | 15 | | 95.127.182.___ | ES | 16 | | 195.77.90.___ | ES | 19 | | 188.86.18.___ | ES | 2 | | 212.145.210.___ | ES | 38 | | 148.3.169.___ | ES | 39 | | 95.16.35.___ | ES | 4 | | 81.202.61.___ | ES | 45 | | 88.7.246.___ | ES | 7 | | 81.36.5.___ | ES | 8 | | 88.14.192.___ | ES | 8 | | 212.97.161.___ | ES | 9 | | 193.248.156.___ | FR | 5 | | 82.34.32.___ | GB | 1 | | 86.180.214.___ | GB | 11 | | 81.108.174.___ | GB | 12 | | 86.11.209.___ | GB | 13 | | 86.150.224.___ | GB | 15 | | 2.102.31.___ | GB | 17 | | 93.152.88.___ | GB | 18 | | 86.178.68.___ | GB | 19 | | 176.248.121.___ | GB | 2 | | 2.97.227.___ | GB | 2 | | 62.49.34.___ | GB | 2 | | 79.64.78.___ | GB | 20 | | 2.126.140.___ | GB | 22 | | 87.114.222.___ | GB | 23 | | 188.29.164.___ | GB | 24 | | 82.11.14.___ | GB | 26 | | 81.168.46.___ | GB | 29 | | 86.136.125.___ | GB | 3 | | 90.199.85.___ | GB | 3 | | 86.177.93.___ | GB | 31 | | 82.32.186.___ | GB | 4 | | 79.68.153.___ | GB | 46 | | 151.226.42.___ | GB | 6 | | 2.123.234.___ | GB | 6 | | 90.217.211.___ | GB | 6 | | 212.159.148.___ | GB | 68 | | 88.111.94.___ | GB | 7 | | 77.98.186.___ | GB | 9 | | 41.222.232.___ | GH | 4 | | 176.63.29.___ | HU | 30 | | 86.47.237.___ | IE | 10 | | 37.46.22.___ | IE | 4 | | 95.83.249.___ | IE | 4 | | 109.79.69.___ | IE | 6 | | 79.176.100.___ | IL | 13 | | 122.175.34.___ | IN | 19 | | 114.143.5.___ | IN | 26 | | 115.112.159.___ | IN | 4 | | 79.62.179.___ | IT | 11 | | 79.53.217.___ | IT | 19 | | 188.216.54.___ | IT | 2 | | 46.44.203.___ | IT | 2 | | 80.86.57.___ | IT | 2 | | 5.170.192.___ | IT | 27 | | 80.23.42.___ | IT | 3 | | 89.249.177.___ | IT | 3 | | 93.39.141.___ | IT | 31 | | 80.183.6.___ | IT | 34 | | 79.25.107.___ | IT | 35 | | 81.208.25.___ | IT | 39 | | 151.57.154.___ | IT | 4 | | 79.60.239.___ | IT | 42 | | 79.47.25.___ | IT | 5 | | 188.216.114.___ | IT | 7 | | 151.31.139.___ | IT | 8 | | 46.185.139.___ | JO | 9 | | 211.180.177.___ | KR | 22 | | 31.214.125.___ | KW | 2 | | 89.203.17.___ | KW | 3 | | 94.187.138.___ | KW | 4 | | 209.59.110.___ | LC | 18 | | 41.137.40.___ | MA | 12 | | 189.211.204.___ | MX | 5 | | 89.98.64.___ | NL | 6 | | 195.241.8.___ | NL | 9 | | 195.1.82.___ | NO | 70 | | 200.46.9.___ | PA | 30 | | 111.125.66.___ | PH | 1 | | 89.174.81.___ | PL | 7 | | 64.89.12.___ | PR | 24 | | 82.154.194.___ | PT | 12 | | 188.48.145.___ | SA | 8 | | 42.61.41.___ | SG | 25 | | 87.197.112.___ | SK | 3 | | 116.58.231.___ | TH | 4 | | 195.162.90.___ | UA | 5 | | 108.185.167.___ | US | 1 | | 108.241.56.___ | US | 1 | | 198.24.64.___ | US | 1 | | 199.249.233.___ | US | 1 | | 204.8.13.___ | US | 1 | | 206.81.195.___ | US | 1 | | 208.75.20.___ | US | 1 | | 24.149.8.___ | US | 1 | | 24.178.7.___ | US | 1 | | 38.132.41.___ | US | 1 | | 63.233.138.___ | US | 1 | | 68.15.198.___ | US | 1 | | 72.26.57.___ | US | 1 | | 72.43.167.___ | US | 1 | | 74.65.154.___ | US | 1 | | 74.94.193.___ | US | 1 | | 75.150.97.___ | US | 1 | | 96.84.51.___ | US | 1 | | 96.90.244.___ | US | 1 | | 98.190.153.___ | US | 1 | | 12.23.72.___ | US | 10 | | 50.225.58.___ | US | 10 | | 64.140.101.___ | US | 10 | | 66.185.229.___ | US | 10 | | 70.63.88.___ | US | 10 | | 96.84.148.___ | US | 10 | | 107.178.12.___ | US | 11 | | 170.253.182.___ | US | 11 | | 206.127.77.___ | US | 11 | | 216.27.83.___ | US | 11 | | 72.196.170.___ | US | 11 | | 74.93.168.___ | US | 11 | | 108.60.97.___ | US | 12 | | 205.196.77.___ | US | 12 | | 63.159.160.___ | US | 12 | | 204.93.122.___ | US | 13 | | 206.169.117.___ | US | 13 | | 208.104.106.___ | US | 13 | | 65.28.31.___ | US | 13 | | 66.119.110.___ | US | 13 | | 67.84.164.___ | US | 13 | | 69.178.166.___ | US | 13 | | 71.232.229.___ | US | 13 | | 96.3.6.___ | US | 13 | | 205.214.233.___ | US | 14 | | 38.96.46.___ | US | 14 | | 67.61.214.___ | US | 14 | | 173.233.58.___ | US | 141 | | 64.251.53.___ | US | 15 | | 73.163.215.___ | US | 15 | | 24.61.176.___ | US | 16 | | 67.10.184.___ | US | 16 | | 173.14.42.___ | US | 17 | | 173.163.34.___ | US | 17 | | 104.138.114.___ | US | 18 | | 23.24.168.___ | US | 18 | | 50.202.9.___ | US | 19 | | 96.248.123.___ | US | 19 | | 98.191.183.___ | US | 19 | | 108.215.204.___ | US | 2 | | 50.198.37.___ | US | 2 | | 69.178.183.___ | US | 2 | | 74.190.39.___ | US | 2 | | 76.90.131.___ | US | 2 | | 96.38.10.___ | US | 2 | | 96.60.117.___ | US | 2 | | 96.93.6.___ | US | 2 | | 74.69.197.___ | US | 21 | | 98.140.180.___ | US | 21 | | 50.252.0.___ | US | 22 | | 69.71.200.___ | US | 22 | | 71.46.59.___ | US | 22 | | 74.7.35.___ | US | 22 | | 12.191.73.___ | US | 23 | | 208.123.156.___ | US | 23 | | 65.190.29.___ | US | 23 | | 67.136.192.___ | US | 23 | | 70.63.216.___ | US | 23 | | 96.66.144.___ | US | 23 | | 173.167.128.___ | US | 24 | | 64.183.78.___ | US | 24 | | 68.44.33.___ | US | 24 | | 23.25.9.___ | US | 25 | | 24.100.92.___ | US | 25 | | 107.185.110.___ | US | 26 | | 208.118.179.___ | US | 26 | | 216.133.120.___ | US | 26 | | 75.182.97.___ | US | 26 | | 107.167.202.___ | US | 27 | | 66.85.239.___ | US | 27 | | 71.122.125.___ | US | 28 | | 74.218.169.___ | US | 28 | | 76.177.204.___ | US | 28 | | 216.165.241.___ | US | 29 | | 24.178.50.___ | US | 29 | | 63.149.147.___ | US | 29 | | 174.66.84.___ | US | 3 | | 184.183.156.___ | US | 3 | | 50.233.39.___ | US | 3 | | 70.183.165.___ | US | 3 | | 71.178.212.___ | US | 3 | | 72.175.83.___ | US | 3 | | 74.142.22.___ | US | 3 | | 98.174.50.___ | US | 3 | | 98.251.168.___ | US | 3 | | 206.74.148.___ | US | 30 | | 24.131.201.___ | US | 30 | | 50.80.199.___ | US | 30 | | 69.251.49.___ | US | 30 | | 108.6.53.___ | US | 31 | | 74.84.229.___ | US | 31 | | 172.250.78.___ | US | 32 | | 173.14.75.___ | US | 32 | | 216.201.55.___ | US | 33 | | 40.130.243.___ | US | 33 | | 164.58.163.___ | US | 34 | | 70.182.187.___ | US | 35 | | 184.170.168.___ | US | 37 | | 198.46.110.___ | US | 37 | | 24.166.234.___ | US | 37 | | 65.34.19.___ | US | 37 | | 75.146.12.___ | US | 37 | | 107.199.135.___ | US | 38 | | 206.193.215.___ | US | 38 | | 50.254.150.___ | US | 38 | | 69.54.48.___ | US | 38 | | 172.8.30.___ | US | 4 | | 24.106.124.___ | US | 4 | | 65.127.169.___ | US | 4 | | 71.227.65.___ | US | 4 | | 71.58.72.___ | US | 4 | | 74.9.236.___ | US | 4 | | 12.166.108.___ | US | 40 | | 174.47.56.___ | US | 40 | | 66.76.176.___ | US | 40 | | 76.111.90.___ | US | 41 | | 96.10.70.___ | US | 41 | | 97.79.226.___ | US | 41 | | 174.79.117.___ | US | 42 | | 70.138.178.___ | US | 42 | | 64.233.225.___ | US | 43 | | 97.89.203.___ | US | 43 | | 12.28.231.___ | US | 44 | | 64.235.157.___ | US | 45 | | 76.110.237.___ | US | 45 | | 71.196.10.___ | US | 46 | | 173.167.177.___ | US | 49 | | 24.7.92.___ | US | 49 | | 68.187.225.___ | US | 49 | | 184.75.77.___ | US | 5 | | 208.91.186.___ | US | 5 | | 71.11.113.___ | US | 5 | | 75.151.112.___ | US | 5 | | 98.189.112.___ | US | 5 | | 69.170.187.___ | US | 51 | | 97.64.182.___ | US | 51 | | 24.239.92.___ | US | 52 | | 72.211.28.___ | US | 53 | | 66.179.44.___ | US | 54 | | 66.188.47.___ | US | 55 | | 64.60.22.___ | US | 56 | | 73.1.95.___ | US | 56 | | 75.140.143.___ | US | 58 | | 24.199.140.___ | US | 59 | | 216.240.53.___ | US | 6 | | 216.26.16.___ | US | 6 | | 50.242.1.___ | US | 6 | | 65.83.137.___ | US | 6 | | 68.119.102.___ | US | 6 | | 68.170.224.___ | US | 6 | | 74.94.231.___ | US | 6 | | 96.64.21.___ | US | 6 | | 71.187.41.___ | US | 60 | | 184.177.173.___ | US | 61 | | 75.71.114.___ | US | 61 | | 75.82.232.___ | US | 61 | | 97.77.161.___ | US | 63 | | 50.154.213.___ | US | 65 | | 96.85.169.___ | US | 67 | | 100.33.70.___ | US | 68 | | 98.100.71.___ | US | 68 | | 24.176.214.___ | US | 69 | | 74.113.89.___ | US | 69 | | 204.116.101.___ | US | 7 | | 216.216.68.___ | US | 7 | | 65.188.191.___ | US | 7 | | 69.15.165.___ | US | 7 | | 74.219.118.___ | US | 7 | | 173.10.219.___ | US | 71 | | 97.77.209.___ | US | 72 | | 173.163.236.___ | US | 73 | | 162.210.13.___ | US | 79 | | 12.236.19.___ | US | 8 | | 208.180.242.___ | US | 8 | | 24.221.97.___ | US | 8 | | 40.132.97.___ | US | 8 | | 50.79.227.___ | US | 8 | | 64.130.109.___ | US | 8 | | 66.80.57.___ | US | 8 | | 74.68.130.___ | US | 8 | | 74.70.242.___ | US | 8 | | 96.80.61.___ | US | 81 | | 74.43.153.___ | US | 83 | | 208.123.153.___ | US | 85 | | 75.149.238.___ | US | 87 | | 96.85.138.___ | US | 89 | | 208.117.200.___ | US | 9 | | 208.68.71.___ | US | 9 | | 50.253.180.___ | US | 9 | | 50.84.132.___ | US | 9 | | 63.139.29.___ | US | 9 | | 70.43.78.___ | US | 9 | | 74.94.154.___ | US | 9 | | 50.76.82.___ | US | 94 | +-----------------+------------+-------------+
In next table we can see the distribution of IP addresses by country:
+--------+ | 214 US | | 28 GB | | 17 IT | | 15 ES | | 15 CA | | 8 DE | | 4 IE | | 3 KW | | 3 IN | | 3 CZ | | 2 NL | | 1 UA | | 1 TH | | 1 SK | | 1 SG | | 1 SA | | 1 PT | | 1 PR | | 1 PL | | 1 PH | | 1 PA | | 1 NO | | 1 MX | | 1 MA | | 1 LC | | 1 KR | | 1 JO | | 1 IL | | 1 HU | | 1 GH | | 1 FR | | 1 EC | | 1 DK | | 1 CR | | 1 CO | | 1 CN | | 1 CH | | 1 BE | | 1 AU | | 1 AR | | 1 AO | +--------+
Based on these tables
