Here you can find answers for various Frequently Asked Questions:

General Questions

Can I analyze URLs with Cuckoo?

New in version 0.5: Native support for URL analysis was added to Cuckoo.

Changed in version 2.0-rc1: Cuckoo will not only start the browser (i.e., Internet Explorer) but will also attempt to actively instrument it in order to extract interesting results such as executed Javascript, iframe URLs, etc. See also our 2.0-rc1 blogpost.

Additional details on URL submissions is documented at Submit an Analysis, but it boils down to:

$ cuckoo submit --url http://www.example.com

Can I use Volatility with Cuckoo?

New in version 0.5: Cuckoo introduces support for optional full memory dumps, which are created at the end of the analysis process. You can use these memory dumps to perform additional memory forensic analysis with Volatility.

Please also consider that we don’t particularly encourage this: since Cuckoo employs some rootkit-like technologies to perform its operations, the results of a forensic analysis would be polluted by the sandbox’s components.

What do I need to use Cuckoo with VMware ESXi?

To run with VMware vSphere Hypervisor (or ESXi) Cuckoo leverages on libvirt or pyVmomi (the Python SDK for the VMware vSphere API). VMware API are used to take control over virtual machines, though these APIs are available only in the licensed version. In VMware vSphere free edition these APIs are read only, so you will be unable to use it with Cuckoo. For the minimum license needed, please have a look at VMware website.


After upgrade Cuckoo stops to work

Probably you upgraded it in a wrong way. It’s not a good practice to rewrite the files due to Cuckoo’s complexity and quick evolution.

Please follow the upgrade steps described in Upgrading from a previous release.

Cuckoo stumbles and produces some error I don’t understand

Cuckoo is a mature but always evolving project, it’s possible that you encounter some problems while running it, but before you rush into sending emails to everyone make sure you read what follows.

Cuckoo is not meant to be a point-and-click tool: it’s designed to be a highly customizable and configurable solution for somewhat experienced users and malware analysts.

It requires you to have a decent understanding of your operating systems, Python, the concepts behind virtualization and sandboxing. We try to make it as easy to use as possible, but you have to keep in mind that it’s not a technology meant to be accessible to just anyone.

That being said, if a problem occurs you have to make sure that you did everything you could before asking for time and effort from our developers and users. We just can’t help everyone, we have limited time and it has to be dedicated to the development and fixing of actual bugs.

  • We have extensive documentation, read it carefully. You can’t just skip parts of it.
  • We have a Discussion page where you can find discussion platforms on which we’re frequently helping our users.
  • We have lot of users producing content on Internet, Google it.
  • Spend some of your own time trying fixing the issues before asking ours, you might even get to learn and understand Cuckoo better.

Long story short: use the existing resources, put some efforts into it and don’t abuse people.

If you still can’t figure out your problem, you can ask help on our online communities (see Final Remarks). Make sure when you ask for help to:

  • Use a clear and explicit title for your emails: “I have a problem”, “Help me” or “Cuckoo error” are NOT good titles.
  • Explain in details what you’re experiencing. Try to reproduce several times your issue and write down all steps to achieve that.
  • Use no-paste services and link your logs, configuration files and details on your setup.
  • Eventually provide a copy of the analysis that generated the problem.

Check and restore current snapshot with KVM

If something goes wrong with virtual machine it’s best practice to check current snapshot status. You can do that with the following:

$ virsh snapshot-current "<Name of VM>"

If you got a long XML as output your current snapshot is configured and you can skip the rest of this chapter; anyway if you got an error like the following your current snapshot is broken:

$ virsh snapshot-current "<Name of VM>"
error: domain '<Name of VM>' has no current snapshot

To fix and create a current snapshot first list all machine’s snapshots:

$ virsh snapshot-list "<Name of VM>"
 Name                 Creation Time             State
 1339506531           2012-06-12 15:08:51 +0200 running

Choose one snapshot name and set it as current:

$ snapshot-current "<Name of VM>" --snapshotname 1339506531
Snapshot 1339506531 set as current

Now the virtual machine state is fixed.

Check and restore current snapshot with VirtualBox

If something goes wrong with virtual it’s best practice to check the virtual machine status and the current snapshot. First of all check the virtual machine status with the following:

$ VBoxManage showvminfo "<Name of VM>" | grep State
State:           powered off (since 2012-06-27T22:03:57.000000000)

If the state is “powered off” you can go ahead with the next check, if the state is “aborted” or something else you have to restore it to “powered off” before:

$ VBoxManage controlvm "<Name of VM>" poweroff

With the following check the current snapshots state:

$ VBoxManage snapshot "<Name of VM>" list --details
Name: s1 (UUID: 90828a77-72f4-4a5e-b9d3-bb1fdd4cef5f)
Name: s2 (UUID: 97838e37-9ca4-4194-a041-5e9a40d6c205) *

If you have a snapshot marked with a star “*” your snapshot is ready, anyway you have to restore the current snapshot:

$ VBoxManage snapshot "<Name of VM>" restorecurrent

Unable to bind result server error

At Cuckoo startup if you get an error message like this one:

2014-01-07 18:42:12,686 [root] CRITICAL: CuckooCriticalError: Unable to bind result server on [Errno 99] Cannot assign requested address

It means that Cuckoo is unable to start the result server on the IP address written in cuckoo.conf (or in machinery.conf if you are using the resultserver_ip option inside). This usually happen when you start Cuckoo without bringing up the virtual interface associated with the result server IP address. You can bring it up manually, it depends from one virtualization software to another, but if you don’t know how to do, a good trick is to manually start and stop an analysis virtual machine, this will bring virtual networking up.

In the case of VirtualBox the hostonly interface vboxnet0 can be created as follows:

# If the hostonly interface vboxnet0 does not exist already.
$ VBoxManage hostonlyif create

# Configure vboxnet0.
$ VBoxManage hostonlyif ipconfig vboxnet0 --ip --netmask

Error during template rendering

Changed in version 2.0-rc1.

In our 2.0-rc1 release a bug was introduced that looks as follows in the screenshot below. In order to resolve this issue in your local setup, please open the web/analysis/urls.py file and modify the 21st line by adding an underscore as follows:

-        "/(?P<ip>[\d\.]+)?/(?P<host>[a-zA-Z0-9-\.]+)?"
+        "/(?P<ip>[\d\.]+)?/(?P<host>[ a-zA-Z0-9-_\.]+)?"

The official fixes for this issue can be found in the following commits.


501 Unsupported Method (‘GET’)

Changed in version 2.0-rc1.

Since 2.0-rc1 Cuckoo supports both the legacy Cuckoo Agent as well as a new, REST API-based, Cuckoo Agent for communication between the Guest and the Host machine. The new Cuckoo Agent is an improved Agent in the sense that it also allows usage outside of Cuckoo. As an example, it is used extensively by VMCloak in order to automatically create, configure, and cloak Virtual Machines.

Now in order to determine whether the Cuckoo Host is talking to the legacy or new Cuckoo Agent it does a HTTP GET request to the root path (/). The legacy Cuckoo Agent, which is based on xmlrpc, doesn’t handle that specific route and therefore returns an error, 501 Unsupported method.

Having said that, the message is not actually an error, it is simply Cuckoo trying to determine to which version of the Cuckoo Agent it is talking.


It should be noted that even though there is a new Cuckoo Agent available, backwards compatibility for the legacy Cuckoo Agent is still available and working properly.


Permission denied for tcpdump

Changed in version 2.0.0.

With the new Cuckoo structure in-place all storage is now, by default, located in ~/.cuckoo, including the PCAP file, which will be stored at ~/.cuckoo/storage/analyses/task_id/dump.pcap. On Ubuntu with AppArmor enabled (default configuration) tcpdump doesn’t have write permission to dot-directories in $HOME, causing the permission denied message and preventing Cuckoo from capturing PCAP files.

One of the workaround is as follows - by installing AppArmor utilities and simply disabling the tcpdump AppArmor profile altogether (more appropriate solutions are welcome of course):

sudo apt-get install apparmor-utils
sudo aa-disable /usr/sbin/tcpdump

DistributionNotFound / No distribution matching the version..

Changed in version 2.0.0.

Installing Cuckoo through the Python package brings its own set of problems, namely that of outdated Python package management software. This FAQ entry targets the following issue..:

$ cuckoo
Traceback (most recent call last):
File "/usr/local/bin/cuckoo", line 5, in <module>
    from pkg_resources import load_entry_point
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 2749, in <module>
    working_set = WorkingSet._build_master()
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 446, in _build_master
    return cls._build_from_requirements(__requires__)
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 459, in _build_from_requirements
    dists = ws.resolve(reqs, Environment())
File "/usr/lib/python2.7/dist-packages/pkg_resources.py", line 628, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: tlslite-ng==0.6.0a3

Those issues - and related ones - are caused by outdated Python package management software. Fortunately their fix is fairly trivial and therefore the following command should do the trick:

pip install -U pip setuptools

IOError: [Errno 24] Too many open files

It is most certainly possible running into this issue when analyzing samples that have a lot of dropped files, so many that the Processing Utility can’t allocate any new file descriptors anymore.

The easiest workaround for this issue is to bump the soft and hard file descriptor limit for the current user. This may be done as documented in the following blogpost.

In case if you using Supervisor set minfds in supervisord.conf.

Remember that you have to login in to a new shell (i.e., usually logout first) session in order for the changes to take effect.


In case you’re installing or upgrading the Cuckoo Package, it has happened before to people that they got an error much like the following:

pkg_resources.ContextualVersionConflict: (HTTPReplay 0.1.5
Requirement.parse('HTTPReplay==0.1.17'), set(['Cuckoo']))

Now this is quite odd, as generally speaking we’ve specifically requested pip to install all dependencies with their exact version (and in fact, if you look at pip freeze you’ll see the correct version), but it does happen sometimes that older versions of various libraries are still around.

The easiest way to resolve this issue is by uninstalling all versions of said dependency and reinstalling Cuckoo. In the case presented above, with HTTPReplay, this may look as follows:

$ sudo pip uninstall httpreplay
Uninstalling HTTPReplay-0.1.17:
Proceed (y/n)? y
Successfully uninstalled HTTPReplay-0.1.17

$ sudo pip uninstall httpreplay
Uninstalling HTTPReplay-0.1.5:
Proceed (y/n)? y
Successfully uninstalled HTTPReplay-0.1.5

$ sudo pip uninstall httpreplay
Cannot uninstall requirement httpreplay, not installed

Then reinstalling Cuckoo again is simply invoking pip install -U cuckoo or similar.

ValueError: incomplete format key

This issue may appear at runtime after tinkering with settings in $CWD/conf, as input is passed to the configuration parser at runtime unescaped. Double-check your configuration files with an eye out for potentially troublesome character combinations such as %(.

Troubleshooting VM network configuration

In case the network configuration of your Virtual Machine isn’t working as expected, you’ll be prompted with the message to resolve this issue as Cuckoo isn’t able to use it for analyses as-is. There are numerous possibilities as to why the network configuration and/or your setup are incorrect so please read our documentation once more. However, most often the issue lies within one of the following reasons:

  • The IP address of the VM has been configured incorrectly. Please verify that the VM has a static IP address, that it matches the one in the Cuckoo configuration, and that the configured network interface exists and is up. Also, in case of VirtualBox, did you configure the network interface to be a Host-Only interface?
  • Check that there are no firewalls in-place that hinder the communication between your Host and Guest and double check that the Host and Guest can ping each other as well as connect to each other.

If connections from the Cuckoo Host to the Guest work, but the other way around don’t, then some additional problems may be at hand:

  • Is the network configuration equivalent on the host and in the VM? If not, e.g., if the VM sees different IP ranges, then you’ll have to configure the resultserver_ip and resultserver_port, for which we have separate documentation.
  • If you’ve modified the Cuckoo Analyzer (located at $CWD/analyzer) this error message may indicate that a syntax error or other exception was introduced, preventing the Analyzer from being properly started, and thus not being able to perform the analysis as expected.

If you’ve triple-checked the above and are still experiencing issues, then please contact us through one of the various communication channels.

Cuckoo says there’s a version 2.1.0?

If you see the message Outdated! Cuckoo Sandbox version 2.1.0 is available now. and you’ve come to this FAQ entry then you’re entirely correct. There is indeed no version 2.1.0, yet (!). However, due to the logic implemented in the version checker of our 2.0-RC1 and 2.0-RC2 releases, the only way to inform our users about our latest releases is by having a “new” major version release (i.e., 2.1.0 or later). We’ve decided that it’s better to sling a little bit of confusion regarding a non-existing version than not mentioning any new versions to our users altogether. So please bear with us and install the latest version :-)

No handlers could be found for logger X in UWSGI log

If you see this message, it means Cuckoo is throwing an error before its loggers are initialized. This might happen if database migration or CWD updates are required.

Start the development web server to see the error:

$ cuckoo web