Posts Tagged ‘blacklist’

Ourmon DNS Blacklist

Saturday, April 26th, 2008

There is a new module in Ourmon, Topn DNS that shows the DNS traffic statistic. It comes with a DNS blacklist feature that needs to be configured. What I am going to show here are how to configure it (which is quite easy), and automate the update by using simple scripting with Shell, Perl.

First of all, this is the how to for DNS blacklist configuration:

The dns_include file config line allows a DNS name based blacklist to be configured into the ourmon probe. Any number of files may be given. The format of individual entries in the DNS blacklist is as follows: A

One entry should be given per line.

DNS query responses are unwrapped and if the question is found to match the DNS name in the blacklist, an ourmon event log message is generated.

That means, we need to create a blacklist file with the format above, and a list of black listed domains.

There is a project called DNS-BH, they create and maintain a listing of domains that are known to be used to propagate malware and spyware. So, with the free malware domains list, we are able to create a list and include it to the DNS blacklist.

I have created 2 scripts, 1 Perl script ( to grab the domains from the malware domains list and write them to a new file with format that Ourmon accepts, for example:

From        unknown      2008apr
to A

and 1 Shell ( script to process the update, so that I am able to set it as cron job.

For those who are interested to try it out, you may download it at
There is a Readme file included the package as well. You need to edit the path of dns_include, and the path in the shell script if your installation is in different directory.

This is the sample of the event log after blacklist has been configured, so you need to check why there were DNS requests to malware domains from these servers. (Click to enlarge the image.)
DNS Blacklist Event Log

There are 2 blacklist features in Ourmon as well, which are IRC blacklist and IP blacklist. Ourmon team has the IRC blacklist script written and put them in Ourmon src/scripts/, and I am still working on IP Blacklist which will fetch the black list IP from Harimau watchlist, the main problem is the support of netblock in the Ourmon IP Blacklist, which I will consider to remove those netblock addresses.

If you concern on the CPU and memory usage, here is the resource usage of Ourmon, with 20290 domains in DNS blacklist, and list of IP from EmergingThreat botcc rules in IRC blacklist loaded, and over 10k/s packets at peaks.

59799   root          1   -58    0  48552K 28348K  bpf    4   3:44   2.49%  ourmon

If you have any other recommendation on DNS blacklist, please let me know.

Ourmon and Snort 2.8.1 Released

Friday, April 4th, 2008

I noticed Ourmon 2.8.1 is quietly released on 21 March 2008. This bug-fix release fixes the bugs that I have reported previously, and my name is in the release note. The IP blacklist config takes 3 argument now, this helps when you have multiple blacklists, so you immediately tell which blacklist caused the message, but I am yet to test this feature.
For example in ourmon.conf:

blist_include "irc"  /home/mrourmon/etc/ipblacklist.txt

Snort LogoSnort, an open source network intrusion prevention and detection system, releases version 2.8.1. I got a 404 error while I was trying to download Snort yesterday and noticed the file was not there anymore. Within few minutes, the Snort download page was refreshed and replaced with new v2.8.1 package. Coincidentally, the release version number is same with Ourmon latest bug-fix release. In v2.8.1, one of the new additions is the ability to read multiple pcaps from the command line, which I have usually done with Argus. Here is the sample:

[[email protected] /]# snort -dv -r irc1.pcap -r irc2.pcap | less
Running in packet dump mode

        --== Initializing Snort ==--
Initializing Output Plugins!
Verifying Preprocessor Configurations!
TCPDUMP file reading mode.
Reading network traffic from "irc1.pcap" file.
snaplen = 65535

        --== Initialization Complete ==--

   ,,_     -*> Snort! <*-
  o"  )~   Version 2.8.1 (Build 28)
   ''''    By Martin Roesch & The Snort Team:
           (C) Copyright 1998-2008 Sourcefire Inc., et al.
           Using PCRE version: 7.6 2008-01-28

07/11-08:00:32.312306 ->
TCP TTL:40 TOS:0x0 ID:51682 IpLen:20 DgmLen:91 DF
***AP*** Seq: 0xB368B2EB  Ack: 0xE79F2A5  Win: 0xB50  TcpLen: 32
TCP Options (3) => NOP NOP TS: 2184210158 757152
3A 62 6D 77 30 37 21 34 76 71 74 71 74 34 40 38  :[email protected]
32 2E 37 39 2E 38 37 2E 37 39 20 4A 4F 49 4E 20 JOIN
23 61 6C 62 61 0D 0A                                               #alba..