Monday, December 29, 2008

Distributed SSH Brute Force Attempts, part 3

I wanted to be able to harvest the log data that the brute force attempts are generating, so I've decided to not move the SSH listening port. I'm also logging each event within my firewall logs. The particular machine I'm seeing the attacks on is a FreeBSD box (I should've mentioned that earlier) and I'm using PF as the firewall of choice.

I'd like to show you my listing of blocked IPs. I've been actively gathering them since approximately 11/17/2008. I was unhappy that I hadn't noticed the distributed attempts until November and wanted more trending data, so I reached into my SSH logs and parsed the files present with a very dirty script that added each unique IP to a PF table that is designed to block such activity. The script is below:

[root@delly ~]# cat IPscript

cd /var/log
bunzip2 pflog.*

cat /var/log/auth.log | grep sshd | grep -i 'invalid user' > /tmp/auth_IP_list_1
bzcat /var/log/auth.log.[01234567].bz2 | grep sshd| grep -i 'invalid user' >> /tmp/auth_IP_list_1
sed '/Failed keyboard-interactive/d' /tmp/auth_IP_list_1 > /tmp/auth_IP_list_2
awk '{print $10}' /tmp/auth_IP_list_2 > /tmp/auth_IP_list_3

tcpdump -nettttr /var/log/pflog > /tmp/fw_IP_list_1
tcpdump -nettttr /var/log/pflog.0 >> /tmp/fw_IP_list_1
awk '{print $9}' /tmp/fw_IP_list_1 > /tmp/fw_IP_list_2
nawk -F. '{print $1, $2, $3, $4}' /tmp/fw_IP_list_2 > /tmp/fw_IP_list_3
sed 's/ /./g' /tmp/fw_IP_list_3 > /tmp/fw_IP_list_4

cat /tmp/fw_IP_list_4 >> /tmp/auth_IP_list_4
cat /tmp/auth_IP_list_4 | sort -rn | uniq > /tmp/auth_IP_list_5
cat /tmp/auth_IP_list_5 | grep -v '' > /tmp/auth_IP_list_6
cat /tmp/auth_IP_list_6 | grep -v '' > /tmp/auth_IP_list_7
cat /tmp/auth_IP_list_7 | grep -v '10.150.1' > /tmp/auth_IP_list_8
cat /tmp/auth_IP_list_8
cat /tmp/auth_IP_list_8 | wc -l

pfctl -t bruteforce -T add -f /tmp/auth_IP_list_8

rm -rf /tmp/fw_IP_list_* /tmp/auth_IP_list_*

I apologize for the lack of comments in the I said, it was an extremely dirty hack that required me to learn a tad of sed and awk. The script outputs the following file:

My logs don't actually go back that far. The FW logs go back to 14 Dec. The SSH service logs go back to 26 Nov. I probably have captured IPs reaching back to the beginning of November, though.

My FW policy prevents anything from entering the network unless specifically allowed (default deny policy). The reason I wanted to track the IPs was because my Denyhosts configuration wasn't catching most of these and it was working fine before this new trend occurred. I'm a security consultant and a researcher at heart, so I thought that tracking this would be cool. My home router has ports 22, 443, and 3306 exposed to the wild for the FreeBSD box. The FW only allows certain IPs in on those ports, though, so nothing will get in. The activity that doesn't get immediately blocked is blocked by the bruteforce_IPtable script that I run daily. The script is flawless and I will begin to have it run hourly via a cronjob. I'll also have it send an updated list to my website daily.

The IPs within my block table number 565. The script parsed 115 from the logs tonight, but only added 1 IP. The norm is usually 2-3 daily. The rest of the IPs are from logs over the last month and a half.

Oh yeah, I've another script does a daily copy of the IPs that are added to the table, so I can at least quickly determine (using 'diff') what was added on a certain day. I can create a script that will show me what was added daily for a given timespan (day/week/month).
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