Know Your Enemy:
Learning with VMware

Building Virutal Honeynets using VMware.

Honeynet Project
Last Modified: 27 January, 2003

Virtual Honeynets are a solution that allow you to run a complete Honeynet with multiple operating systems on the same physical computer. First discussed in the paper Know Your Enemy: Virtual Honeynets, these solutions have the advantage of being easier to deploy and simpler to manage. The Honeynet Project has also found VMware to make an excellent development environment for Honeynet technologies. In this paper, we will take you through step-by-step how to build and deploy such a solution using the commercial software VMware. In this case, we will build a GenII (2nd Generation) Virtual Honeynet with five different honeypots. It is assumed you have read and understand the concepts discussed in both KYE: Virtual Honeynets and KYE: Honeynets. Also, if this is the first time you have ever worked with Honeynet technologies, it is highly recommended you work in a lab environment. Last, as with all virtual software, you need to be aware of the risk of attackers identifying, and potentially breaking out of, the virtual environment. You have been warned.

Plan of Attack
The format of this paper is similar to KYE: User-Mode Linux, its broken down into five parts. In the first part we will describe what VMware is, how it works, and how to install it. In the second part, we describe how to configure VMware and install your honeypots. In the third part we describe how to implement Data Control on your VMware Honeynet using IPTables. In the fourth part we describe how to implement Data Capture using Snort. Finally, in the fifth part, we describe how to test your setup.

Part I: VMware
VMware is virtualization software that allows you to run multiple operating systems at the same time. Unlike User-Mode Linux, VMware allows you to run different operating systems, as long as they can run on Intel X86 architecture. Developed and sold by VMware Inc, there are actually three different software products you can choose; Workstation, GSX, or ESX. Of the three, we will be using GSX. GSX is more powerful then Workstation, designed to run more then two operating systems at the same time and supports remote administration. However, most of the information discussed here can also be applied to Workstation. For the purpose of this paper, we are going to build our Virtual Honeynet on a laptop, specifically an IBM Thinkpad T23, utilizing a PIII 1Ghz processor and 768 MB RAM. The base operating system is Red Hat 7.3.

VMware works by installing virtualization software on your computer. This virtualization software then allows you to boot and run multiple operating systems at the same time. The very first operating system you install, the base OS, is called the HostOS. This is the operating system you install VMware on. Once you have installed the HostOS and VMware, you can then install additional operating systems that run within the virtual environment. All of these additional operating systems are called the GuestOS's, as they are 'guests' on the Host operating system. To get a better understanding of how this works, refer to Figure 1. Installing VMware on our Linux HostOS is very easy, you simply install a single RPM package. The command looks similar to this.

host #rpm -vi VMware-gsx-2.0.1-2129.i386.rpm
Preparing packages for installation...

There are additional software packages we can install, such as the remote administration package. However, our laptop does not require this as all administration will be done locally. For more information on these additional packages, refer to the VMware documentation.

Part II: Configuring VMware and Installing your Honeypots
Once installed, the next step is to configure the VMware software. Configuration is done by executing the command ''. During the configuration process, VMware will most likely have to recompile several of its own kernel modules. This means you need both a compiler and the source code for your kernel. On our laptop, we are running kernel 2.4.18-19.7.x. We then confirm we have the source code.

host #uname -r
host #
host #rpm -qa | grep source
marge $ls -l /usr/src
total 8
lrwxrwxrwx    1 root     root           19 Dec 26 13:53 linux-2.4 -> linux-2.4.18-19.7.x
drwxr-xr-x   17 root     root         4096 Dec 26 13:53 linux-2.4.18-19.7.x
drwxr-xr-x    7 root     root         4096 Jul 12 11:52 redhat

Once you have the source code installed, you can begin the installation. During the process, the only real option is Networking, which we want. Remember, the goal is to have all the GuestOS's route through the HostOS, our gateway. During the installation process, select Networking. Later in the installation process, you will be asked if you want HostOnly networking. Select this option also, and give the interface an IP address. This is the gateway IP address, which we will be using Linked below is the series of commands executed during the configuration process.

Once you have completed the configuration process, VMware should now be running. However, we have one problem. During the default configuration, VMware enabled three interfaces; vmnet0, vmnet1, and vmnet8. Of those three networking interfaces, we want only one interface, vmnet1. vmnet0 is used for bridging, so the GuestOS talks directly to the network, bypassing the HostOS. vmnet8 is used for NAT Networks. Only vmnet1 gives us the control of having the GuestOS's go through the HostOS. Thus, we have to run again, then using the editor, remove the two unwanted interfaces vmnet0 and vmnet8. (being ran for the second time)

Once you have configured VMware, the next step is to install and configure the individual honeypots. For our Honeynet, we are going to install and run five different honeypots. The requirements for running so many operating systems is not as intensive as you may think. Think about it, no one is going to be using them except attackers, so there is little system activity. Also, for the Unix based systems, there is no need for a GUI, you can administer the systems at the Command Line Interface. Thus, no need for running X-Windows. As such, memory requirements are minimal. Also, each operating system needs no more the 2 GB of hard drive space.

Installing the individual honeypots is simple. First, make sure the vmware virtualization software is running with "ps aef | grep vmnet" and that you have the interface vmnet1 "ifconfig -a". Once you have confirmed that is running, create a new VMware window to install your honeypot. The command is

host #vmware -G &

When you start the Window, you have the option of selecting an existing GuestOS to boot up, or start the installation of a new GuestOS. For installing a new GuestOS, select "Run the Configuration Wizard". Here you select which type of GuestOS you are installing, the directory you will store the file system, create a new virtual disk for the OS, size, enable the CDROM (be sure to disable the floppy, unless its attached) and HostOnly networking. Once you have configured the GuestOS, you simply insert the installation CDROM of the Guest operating system, and Power On the system. From there, the boot and installation of the GuestOS is as you normally would with any operating system. You then proceed to repeat these steps for all five GuestOS honeypots. Once installed, you have the option of installing VMware tools on the honeypots. This helps increase the resolution of the GUI interface. For the Unix systems, you do not need VMware tools, as you can administer from the command line. For Window based honeypots, may want to install this on the honeypots to increase resolution, however, it will be easier for attackers to fingerprint the system as a VMware virtual system. For more information on VMware configuration and GuestOS installation, refer to the VMware documentation.

Before we go any further, you will want to backup your installed honeypots. VMware stores each of your honeypots in a seperate file under its own directory. To backup each honeypot, you only merely have to copy these files. This makes recovering or rebuilding your honeypot extremly easy. With traditional Honeynets, after a honeypot has been compromised and you are done analyzing the attack, you have to rebuild the honeypot before putting it back online. This can be a time consuming process. However, with VMware, rebuilding a honeypot is as simple as copying over your backups. You can have your honeypots up and running within seconds. For example, VMware by default stores the images of each honeypot under the directory /root/vmware. You can backup all of the honeypots by copying this directory. Whenever you want to rebuild a honeypot, you can merely copy over the honeypot directory containing its files.

host #ls -l /root/vmware
total 28
drwxr-xr-x    2 root     root         4096 Oct 10 01:10 linux-6.2
drwxr-xr-x    2 root     root         4096 Jan 14 19:00 linux-7.2
drwxr-xr-x    2 root     root         4096 Jan 14 22:14 linux-7.3
drwxr-xr-x    2 root     root         4096 Jan 25 15:15 openbsd
drwxr-xr-x    2 root     root         4096 Jan 25 15:15 solaris
drwxr-xr-x    2 root     root         4096 Dec 16 08:47 win2000Serv
drwxr-xr-x    2 root     root         4096 Jan 25 15:15 winXPPro
host #
host #cp -a /root/vmware /root/vmware-backup

Part III: Data Control
Once you have setup VMware and the honeypots, the next step is Data Control. The purpose of Data Control is to contain what the attacker can do inbound and outbound of the Honeynet. Typically, we allow anything inbound to the Honeynet systems, but limit outbound connections. For the purpose of this paper, we will use IPTables, an OpenSource firewall solution that comes with Linux. IPTables is a highly flexible stateful firewall, including the ability for connection limiting, network address translation, logging, and many other features. We will configure IPTables to act as a filter on our HostOS, counting outbound packets. Once a limit has been met for outbound connections, all further attempts are blocked, preventing the compromised honeypot from harming other systems. Configuring and implementing these capabilities can be extremely complex. However, the Honeynet Project has develop an IPTables script called rc.firewall that does all the work for you. You merely have to modify the script variables as they apply to your Honeynet, then run the script.

The first thing you have to decide is if you want your gateway to run in layer three routing mode, or layer two bridging mode. Layer two bridging (also known as GenII, or 2nd generation) is the preferred method. When your gateway is acting as a bridge, there is no routing or TTL decrement of packets, it acts as an invisible filtering device, making it much more difficult for attackers to detect. However, for IPTables to work in bridging mode, your kernel must be patched to support it. By default, most kernels do not support IPTables in bridging mode. Red Hat kernel 2.4.18-3 is one of the few that does support this by default. If you want to patch your kernel, you can find the patch at For the purpose of this paper, we will assume your kernel DOES support IPTables in bridging mode. If your kernel does not support bridging mode, the refer to the paper KYE: UML for more information on configuring the rc.firewall script for layer three routing.

Lets cover how to configure the rc.firewall script to implement GenII functionality. There are two critical areas to configure, the networking issues and control issues. Actually, networking is much simpler in bridging mode then in routing mode. In bridging mode there is no routing, nor any Network Address Translation issues. We simply convert the HostOS to a bridge, and the GuestOS's interact directly with other networks. For connection issues, we have to configure how many outbound connections we allow. The options we will have to configure are as follows. First, you will need to set the public IP addresses of the Guest operating systems. These are the IP addresses that hackers will attack, the valid IP addresses of our honeypots. Since we have five honeypots, we will need to list the five IP addresses. The firewall filters need to know who they are.


Second, you will need to identify the name of the internal interface of the HostOS. By default, this is eth1. However, we are using the virtual interface vmnet1, and have to modify this variable.


Third, since we are building a GenII Honeynet, you may want to consider trying Snort-Inline capabilities to drop known outbound attacks. It is beyond the scope of this paper to describe the details of Snort-Inline, that will be discussed in the future paper Know Your Enemy: GenII Honeynet. However, you may want to consider using the Honeynet Snort-Inline Toolkit, which has static, precompiled binaries, configuration files, rulebases, and documentation, which you will find . in the Honeynet Tools section. If you do want to test this capability, you will need to enable the QUEUE option. NOTE: If you enable this option, you MUST be running Snort-Inline, or ALL outbound packets will be dropped. If you are not sure at this point, do NOT enable this feature.

#QUEUE="yes" # Use experimental QUEUE support
QUEUE="no" # Do not use experimental QUEUE support

These are the minimum variables you will want to consider, there may be others depending on the configuration of your system. There are additional options you can update, such as remote management, limiting what connections the firewall can initiate, and giving your honepyots unrestricted DNS access. Also, by default, the script limits each honeypot to the following outbound connections per hour; 9 TCP connections, 20 UDP connections, 50 ICMP connections, and 10 IP other. Details of the script are beyond the scope of this paper. To better understand these variables, we recommend you review the script in detail and try out the different options in a lab environment. Once you have configured the rc.firewall script, you implement it by executing the script. Remember, you are going to be putting your HostOS into bridging mode. For this, your HostOS must have the bridging utilities. For Red Hat systems, this is known as "bridge-utils-0.9.3-4".

There are two gotchas when using bridging. First, you have to boot up all of your GuestOS's before enabling bridging. When the GuestOS's boot, they look for and use the vmnet1 interface. If this interface has already been set to bridging mode, the GuestOS will not find the interface and cannot talk to the network. So, start all of your honeypots BEFORE you run the rc.firewall script. The second gotcha is time, it takes about 10-30 seconds for the bridging to take effect. You have to give the bridge time to learn where all the MAC's are before it can start bridging packets.

host #/.rc.firewall

To confirm the script was successful, there are several things to check. First, ensure that bridging has been enabled. You can confirm this by checking your /var/log/messages file, your kernel should log going into bridging mode. Second, you should have a new interface called 'br0', which is your bridge. Third, use the 'brctl' command to see what interfaces are bound to the bridge. Fourth, your external and internal interfaces will no longer have an IP address, as they are now in bridging mode. Last, review your IPTables rules to ensure you are filtering connections.

host #tail /var/log/messages

host #ifconfig -a

host #brctl show

host #iptables -L -n

If successful, your Data Control is in place. There are also other options for implementing Data Control, such as bandwidth throttling.

Part IV: Data Capture
Once we have completed Data Control, the next step is Data Capture. The purpose of Data Capture is to capture all of the attacker's activity, without them knowing. There are a variety of methods to implement this, however we will focus on two, IPTable logs and Snort. IPTable logs are the logs generated by the firewall whenever there is an inbound or outbound connection. Snort is an OpenSource IDS solution which we will use to capture all network activity, and generate alerts for known attacks.

For IPTables, the logging has already been configured for us with the rc.firewall script. It is configured to log all new inbound and outbound connection to /var/log/messages. Any inbound connection is an indication of a probe, scan, or attack. Any outbound connection indicates that a honeypot has been compromised. The value of IPTable logs is one primarily for alerting. The logs do not have enough information to tell us what the attacker is doing. For Snort, we configure it to capture every packet and its full payload that enters or leaves the Honeynet. Linked here is a Snort config file that will capture and log attacker activity.. You will find a simple Snort startup script that starts Snort and uses the recommended Snort config file. Be sure to update the startup script to monitor the vmnet1 interface of the HostOS. You will most likely want to run this script daily, running the script from cron.

host #./

Since this is a GenII Honeynet, you may want to consider using more advance Data Capture techniques, such as Sebek. This allows you to capture the attacker's activities from kernel space. There are also a variety of other options for implementing Data Capture which are beyond the scope of this paper. For additional options, check out Honeynet Tools Section.

Part V: Testing Your VMware Honeynet
The fifth, and final step, of building our VMware Honeynet is to test our configuration, specifically Data Control and Data Capture. We want to ensure that our Honeynet requirements are behaving as expected. Testing Data Control is relatively simple. We want to ensure that any attempt by the honeypot to initiate an outbound connection is both logged and controlled. By logged, all connection attempts should log an entry to /var/log/messages, alerting us that an outbound connection has been initiated, and the honeypot has most likely been compromised. Also, once the limit has been met, we want to ensure that no more outbound connections are allowed. There is one trick to testing our Honeynet, since we are bridging we need a second computer, the attacker. The bridge will not forward any packets if it cannot match the destination IP to a valid MAC address. If no packets are forwarded, we cannot test IPTables. For those of you who don't have a second computer (or who are just hard core geeks), you can run a second computer virtually by starting up a UML system. The UML system will bind to the tap0 virtual interface, while all of our VMware honeypots will bind to the vmnet1 virutal interface. This way your HostOS is bridging two different virtual networks. Remember, you will have to modify your rc.firewall script with tap0 being the external interface. To learn more about running UML, refer to the paper KYE: UML. The UML can be the attacker, probing the VMware honeypots. For the purpose of this paper, that is the testing concept we will demonstrate. Our UML attacker's IP address will be Yes, this really does work :)

We will test outbound TCP connections, which by default are limited to 9 attempts per hour. To test this we will need two terminal windows open. First we open a terminal on the HostOS and monitor the IPTable logs in /var/log/messages. When we initiate outbound connections from the GuestOS through our Host gateway, we should see the attempts logged there. This information is critical for alerting purposes, indicating the honeypot has been hacked, and the attacker (or automated tool) is attempting outbound connections. Starting with the 10th outbound attempt, the TCP connections should be blocked (the limit was met) and logged. Below is the command you want to execute before attempting any outbound connection.

host #tail -f /var/log/messages

Next, open a terminal on the honeypot system, our GuestOS. Initiate a variety of outbound TCP connections to the external IP, in this case (our UML systems). You will most likely have to repeat the attempts several times.

telnet: connect to address Connection refused

If you see the attempts logged, and blocked after the limit, you have successfully implemented Data Control. Next, we want to ensure that Data Capture is happening, specifically that the Snort process is capturing all packets and their full payload that are entering and leaving the Honeynet. A Snort process should be monitoring the internal interface of the HostOS, specifically vmnet1. To test this, attempt to ping the external system, in this case once again

guest #ping -c 3

The Snort process should have captured the three ICMP Echo Request packets and their full payload. It should have logged the activity to tcpdump binary log format. To confirm, review the log file, an example is below. What is critical is that you are not only capture every packet and its header, but you are capturing the fully payload of every packet.

host #snort -vdr *snort.log

Thats it! You have just completed a very basic test of your Data Control and Data Capture capabilities. There are far more advance tests you can attempt, such as using a second, seperate computer to act as a system on the Internet and interact with the honeypot. However that is beyond the scope of this paper.

Note: As this paper was going through the final review phase, the Project has begun using one of VMware's other features for advance forensic analysis. Specifically, the Suspend feature of VMware. Suspend allows you to literally suspend a GuestOS (or honeypot) image. It freezes all the running processes and saves the memory image to a file. This means you can Suspend your honeypot, turn off your computer, turn it on a week later, bring back up the honeypot, un-suspend it, and you will have it exactly where it was before. This has some incredible forensic applications. The Project has begun saving suspended images of hacked computers, then sending those images to others for analysis. This allows us to analyze a hacked honeypot while its still in its running state. The concern here is when analyzing suspended images, you have to ensure you are doing this on an isolated network, or your hacked honeypot will attempt to connect to any systems it was communicating with before being suspended.

The purpose of this paper was to describe step by step how to build a virtual Honeynet using VMware virtualization software. The goal is to build an entire Honeynet on a single computer. The advantage with VMware is you can run many different types of operating systems at the same time. If you would like to try building your own VMware honeynet, you can get an eval copy of VMware at

The Honeynet Project