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Recently, I wrote an article about How to scan your Linux-Distro for Root Kits . Now that the machine is... clean ! I think, a good thing TO-DO, is to ...
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- 05-06-2006 #1
How to test your Linux-Distro FIREWALL !
Now that the machine is... clean! I think, a good thing TO-DO, is to test my Firewall (AGAIN !!!)
The good news are that we can use the free tool FTester.
The bad news are that FTester needs to be configured right...
So... Let's get to work !
What is FTester ?
The Firewall Tester (FTester) is a tool designed for testing firewalls filtering policies and Intrusion Detection System (IDS) capabilities.
The tool consists of two perl scripts, a packet injector (ftest) and the listening sniffer (ftestd).
The first script injects custom packets, defined in ftest.conf, with a signature in the data part while the sniffer listens for such marked packets.
The scripts both write a log file which is in the same form for both scripts.
A diff of the two produced files (ftest.log and ftestd.log) shows the packets that were unable to reach the sniffer due to filtering rules if these two scripts are ran on hosts placed on two different sides of a firewall.
Stateful inspection firewalls are handled with the 'connection spoofing' option.
A script called freport is also available for automatically parse the log files.
The IDS (Intrusion Detection System) testing feature can be used either with ftest only or with the additional support of ftestd for handling stateful inspection IDS, ftest can also use common IDS evasion techniques.
Instead of using the configuration syntax currently the script can also process snort rule definition file.
- firewall testing
- IDS testing
- simulation of real tcp connections for stateful inspection firewalls and IDS
- connection spoofing
- IP fragmentation / TCP segmentation
- IDS evasion techniques
The following perl modules are required: Net::RawIP, Net::PcapUtils, NetPacket
So... we will need the Net::RawIP , Net::PcapUtils, and NetPacket Perl modules. We may also need the Net::Pcap module if it is not already installed, because the Net::PcapUtils module depends on it.
If we have the CPAN Perl module, we may install these modules with the following commands from shell:
# perl -MCPAN -e "install Net::RawIP" # perl -MCPAN -e "install Net::Pcap" # perl -MCPAN -e "install Net::PcapUtils" # perl -MCPAN -e "install NetPacket"
The most recent release is ftester-1.0.tar.gz (2006-Feb-13). From shell run...
# wget http://dev.inversepath.com/ftester/ftester-1.0.tar.gz
Use tar to... unzip the source code. From shell run...
# tar -xzf ftester-1.0.tar.gz
We have installed a few perl modules required, we have downloaded ftester-1.0.tar.gz (2006-Feb-13) and we have extracted the file and made the directory ftester-1.0.
Well done !!!
We will need to create a configuration file to tell ftest what packets it should generate.
The definition of the packets we want to send for test if they can traverse the firewall is mainly specified in a configuration file (ftest.conf), the main syntax is:
Source Address:Source Port:Destination Address:Destination Port:Flags:Protocol:Type of Service
Source Address:Source Port:Destination Address:Destination Port:Flags:ICMP:icmp_type:icmp_code
a few examples:
# SYN packet to 10.1.7.1 port 80 192.168.0.10:1024:10.1.7.1:80:S:TCP:0 # PSH,ACK reply from 192.168.0.10 192.168.0.10:20:10.1.7.1:1022:AP:TCP:22 # UDP packet 192.168.0.10:53:10.1.7.1:53::UDP:0 # ICMP packet type 3 code 5 192.168.0.10::10.1.7.1:::ICMP:3:5 # ranges are allowed for source address, source port, destination port # source address can also be specified in CIDR form 192.168.0.1-255:1024:10.1.7.1:22:S:TCP:0 192.168.0.1:1024:10.1.7.1:1-65535:S:TCP:0 192.168.0.1:1-1024:10.7.0.1:20-25:S:TCP:22 192.168.3.0/24:1-1024:10.7.0.1:20-25:S:TCP:0 192.168.0.0/22:1024:10.7.0.1:80:S:TCP:0
Now from shell...
# vi ftest.conf
# checking privileged ports (<1025) 192.168.0.10:1025:10.1.7.1:1-1025:S:TCP:0 # checking proxy port 192.168.0.10:1025:10.1.7.1:3128:S:TCP:0 stop_signal=192.168.0.10:80:10.1.7.1:1025:AP:TCP:0
# ./ftestd -i eth0
# ./ftest -f ftest.conf
# ./freport ftest.log ftestd.log
Authorized packets: ------------------- 21 - 192.168.0.10:1025 > 10.1.7.1:21 S TCP 0 22 - 192.168.0.10:1025 > 10.1.7.1:22 S TCP 0 23 - 192.168.0.10:1025 > 10.1.7.1:23 S TCP 0 25 - 192.168.0.10:1025 > 10.1.7.1:25 S TCP 0 80 - 192.168.0.10:1025 > 10.1.7.1:80 S TCP 0 110 - 192.168.0.10:1025 > 10.1.7.1:110 S TCP 0 113 - 192.168.0.10:1025 > 10.1.7.1:113 S TCP 0 1027 - 192.168.0.10:80 > 10.1.7.1:1025 PA TCP 0 Modified packets (probably NAT): -------------------------------- 443 - 192.168.0.10:1025 > 10.1.7.1:443 S TCP 0 443 - 192.168.0.10:1025 > 10.1.7.5:443 S TCP 0 Filtered or dropped packets: ---------------------------- 1 - 192.168.0.10:1025 > 10.1.7.1:1 S TCP 0 2 - 192.168.0.10:1025 > 10.1.7.1:2 S TCP 0 3 - 192.168.0.10:1025 > 10.1.7.1:3 S TCP 0 ... ... ... 1026 - 192.168.0.10:1025 > 10.1.7.1:3128 S TCP 0
A good idea is to run ftest each time you make changes to your firewall, or from time to time just to make sure that your firewall works !!!
Man page (ftester.
I don't think is a good idea to post the results of my test !!!