Per-Analysis Network Routing

Since Cuckoo 2.0-rc1 it is possible to feature per-analysis network routing. In other words, if you have one VM and three samples to analyze, it is possible to deny internet access for the first analysis, route the second analysis through a VPN, and pull the third analysis through the Tor network.

However, aside from the more advanced per-analysis routing, it is naturally also possible to have one default route - a setup that used to be popular before, when the more luxurious routing was not yet available.

In our examples we’ll be focusing on VirtualBox as it is our default machinery choice.

Simple Global Routing

Before delving into the more complex and feature-rich per-analysis network routing we’ll first cover the older approach, which is based on global iptables rules that are, once set, not changed anymore.

In the following setup we’re assuming that the interface assigned to our VirtualBox VM is vboxnet0, the IP address of our VM is (in a /24 subnet), and that the outgoing interface connected to the internet is eth0. With such a setup, the following iptables rules will allow the VMs access to the Cuckoo host machine ( in this setup) as well as the entire internet as you would expect from any application connecting to the internet.

$ sudo iptables -t nat -A POSTROUTING -o eth0 -s -j MASQUERADE

# Default drop.
$ sudo iptables -P FORWARD DROP

# Existing connections.
$ sudo iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT

# Accept connections from vboxnet to the whole internet.
$ sudo iptables -A FORWARD -s -j ACCEPT

# Internal traffic.
$ sudo iptables -A FORWARD -s -d -j ACCEPT

# Log stuff that reaches this point (could be noisy).
$ sudo iptables -A FORWARD -j LOG

And that’s pretty much it, with these rules set we’re almost good to go. However, these rules won’t be doing any packet forwarding unless IP forwarding is explicitly enabled in the kernel. To do so, there is a temporary method that survives until a shutdown or reboot, and a permanent method that is taken into account when booting the machine. Simply put, generally speaking you’ll want to run both commands:

$ echo 1 | sudo tee -a /proc/sys/net/ipv4/ip_forward
$ sudo sysctl -w net.ipv4.ip_forward=1

Iptables rules are not persistent between reboots, so if want to keep them you should use a script or just install iptables-persistent.

Newer Linux distributions have adopted udev’s interface-naming scheme. It’s important to note that this means eth0 may no longer be your primary interface. Possible interface names include ensXX, enp0sXX, and emXX, where the XX part identifies a number. This is particularly important to note for the NAT statement above.

Per-Analysis Network Routing Options

Having discussed the old school method for routing analyses through a network interface we will now walk through the dynamic network routing components that allow for much more granular network routing.

As outlined in the introduction for this chapter of the documentation it has been possible since Cuckoo 2.0-rc1, when we introduced the Cuckoo Rooter, to do per-analysis network routing. Since then various bugs have been resolved and more network routing options have been added.

Following is the list of available routing options.

Routing Option Description
None Routing No routing whatsoever, the only option that does not require the Cuckoo Rooter to be run (and therefore also the default routing option).
Drop Routing Completely drops all non-Cuckoo traffic, including traffic within the VMs’ subnet.
Internet Routing Full internet access as provided by the given network interface (similar to the Simple Global Routing setup).
InetSim Routing Routes all traffic to an InetSim instance - which provides fake services - running on the host machine.
Tor Routing Routes all traffic through Tor.
VPN Routing Routes all traffic through one of perhaps multiple pre-defined VPN endpoints.

Using Per-Analysis Network Routing

Having knowledge about the available network routing options it is time to actually use it in practice. Assuming Cuckoo has been configured properly taking advantage of its features is really as simple as starting the Cuckoo Rooter and choosing a network routing option for your analysis.

Documentation on starting the Cuckoo Rooter may be found in the Cuckoo Rooter Usage document.

Both global routing and per-analysis routing require ip forwarding to be enabled:

$ echo 1 | sudo tee -a /proc/sys/net/ipv4/ip_forward $ sudo sysctl -w net.ipv4.ip_forward=1

Configuring iproute2

For Linux kernel TCP/IP source routing reasons it is required to register each of the network interfaces that we use with iproute2. This is trivial, but necessary.

As an example we’ll be configuring Internet Routing (aka the dirty line) for which we’ll be using the eth0 network interface - reverting back to Ubuntu 14.04 and older terminology here for a second (Ubuntu 16.04 uses network interface names based on the hardware manufacturer, as you will likely have seen happen on BSD-based systems since forever).

To configure iproute2 with eth0 we’re going to open the /etc/iproute2/rt_tables file which will look roughly as follows:

# reserved values
255     local
254     main
253     default
0       unspec
# local

Now roll a random number that is not yet present in this file with your dice of choice and use it to craft a new line at the end of the file. As an example, registering eth0 with iproute2 could look as follows:

# reserved values
255     local
254     main
253     default
0       unspec
# local

400     eth0

And that’s really all there is to it. You will have to do this for each network interface you intend to use for network routing.

None Routing

The default routing mechanism in the sense that Cuckoo allows the analysis to route as defined by a third party. As in, it literally doesn’t do anything. One may use the none routing in conjunction with the Simple Global Routing.

Drop Routing

The drop routing option is somewhat like a default None Routing setup (as in, in a machine where no global iptables rules have been created providing full internet access to VMs or so), except that it is much more aggressive in actively locking down the internet access provided to the VM.

With drop routing the only traffic possible is internal Cuckoo traffic and hence any DNS requests or outgoing TCP/IP connections are blocked.

Internet Routing

By using the internet routing one may provide full internet access to VMs through one of the connected network interfaces. We also refer to this option as the dirty line due to its nature of allowing all potentially malicious samples to connect to the internet through the same uplink.


It is required to register the dirty line network interface with iproute2 as described in the Configuring iproute2 section.

InetSim Routing

For those that have not heard of InetSim, it’s a project that provides fake services for malware to talk to. In order to use InetSim routing one will have to setup InetSim on the host machine (or in a separate VM) and configure Cuckoo so that it knows where to find the InetSim server.

The configuration for InetSim is self-explanatory and can be found as part of the $CWD/conf/routing.conf configuration file:

enabled = yes
server =

In order to quickly get started with InetSim it is possible to download the latest version of the REMnux distribution which features - among many other tools - the latest version of InetSim. Naturally this VM will require its own static IP address which should then be configured in the routing.conf configuration file.

Tor Routing


Although we highly discourage the use of Tor for malware analysis - the maintainers of Tor exit nodes already have a hard enough time keeping up their servers - it is in fact a well-supported feature.

First of all Tor will have to be installed. Please find instructions on installing the latest stable version of Tor here.

We’ll then have to modify the Tor configuration file (not talking about Cuckoo’s configuration for Tor yet!) In order to do so, we will have to provide Tor with the listening address and port for TCP/IP connections and UDP requests. For a default VirtualBox setup, where the host machine has IP address, the following lines will have to be configured in the /etc/tor/torrc file:


Don’t forget to restart Tor (/etc/init.d/tor restart). That leaves us with the Tor configuration for Cuckoo, which may be found in the $CWD/conf/routing.conf file. The configuration is pretty self-explanatory so we’ll leave filling it out as an exercise to the reader (in fact, toggling the enabled field goes a long way):

enabled = yes
dnsport = 5353
proxyport = 9040

Note that the port numbers in the /etc/tor/torrc and $CWD/conf/routing.conf files must match in order for the two to interact correctly.

VPN Routing

Last but not least, it is possible to route analyses through a number of VPNs. By defining a couple of VPNs, perhaps ending up in different countries, it may be possible to see if potentially malicious samples behave differently depending on the country of origin of its IP address.

The configuration for a VPN is much like the configuration of a VM. For each VPN you will need one section in the $CWD/conf/routing.conf configuration file detailing the relevant information for the VPN. In the configuration the VPN will also have to be registered in the list of available VPNs (exactly the same as you’d do for registering more VMs).

Configuration for a single VPN looks roughly as follows:

# Are VPNs enabled?
enabled = yes

# Comma-separated list of the available VPNs.
vpns = vpn0

# Name of this VPN. The name is represented by the filepath to the
# configuration file, e.g., cuckoo would represent /etc/openvpn/cuckoo.conf
# Note that you can't assign the names "none" and "internet" as those would
# conflict with the routing section in cuckoo.conf.
name = vpn0

# The description of this VPN which will be displayed in the web interface.
# Can be used to for example describe the country where this VPN ends up.
description = Spain, Europe

# The tun device hardcoded for this VPN. Each VPN *must* be configured to use
# a hardcoded/persistent tun device by explicitly adding the line "dev tunX"
# to its configuration (e.g., /etc/openvpn/vpn1.conf) where X in tunX is a
# unique number between 0 and your lucky number of choice.
interface = tun0

# Routing table name/id for this VPN. If table name is used it *must* be
# added to /etc/iproute2/rt_tables as "<id> <name>" line (e.g., "201 tun0").
# ID and name must be unique across the system (refer /etc/iproute2/rt_tables
# for existing names and IDs).
rt_table = tun0


It is required to register each VPN network interface with iproute2 as described in the Configuring iproute2 section.