MonkeyFist Fu: The Intro

MonkeyFist Image

MonkeyFist is a dynamic request attack tool. It allows you to do some interesting things with various forms of cross-site requests and play them back to the user’s browser. These requests may contain session information bypassing Cross-Site Request Forgery protection mechanisms. It’s really a lot more simple than it seems.

MonkeyFist is basically a small web server that performs some attacks on the data it receives based on information you provide in the payloads.xml file. To do a deeper dive in to the issues that MonkeyFist exploits you can refer to the white paper we wrote prior to Black Hat on Dynamic CSRF located on the docs page of Hexsec

The best way to get familiar with MonkeyFist is just to dive right in. If you haven’t done so, you can go here to download it from the Hexsec Labs page

MonkeyFist requires you be intimately familiar with the request you want to forge. This should be painfully obvious because you need to tell the tool how to construct the request in order for it to be successful.

The Files

There isn’t much to MonkeyFist, all of the files are pretty small. There are a few items in the zip file, but you really only need to worry about and payloads.xml. All of the configuration for payloads in MonkeyFist is done through payloads.xml. We will get in to syntax in another post. In case you didn’t notice the .py extension, MonkeyFist is written in Python. So if your operating system doesn’t have Python installed (Probably just Windows systems) you are going to need it. I suggest version 2.5 or greater. The version that comes with most Linux distributions and OSX is fine. As a final note about the files, ensure that you run MonkeyFist from the same directory as the other files that come with it. Otherwise, it won’t know where they are located ;)


In the beginning there were no further dependencies but I a saw it was necessary to potentially need to do some more complex parsing for the fixation payload. For that reason I decided to add lxml. I could have gotten away with a more simple parser, but was trying to think ahead a bit. To use the Fixation payload you are going to need to install a 2.x version of lxml. This would be different depending on your operating system. If you are using Ubuntu / Debian don’t just to to apt install lxml, it will give you an old version. Python setuptools helps a lot, it’s just a good idea to use that anyway.

For OSX Leopard (Make sure you have the development tools installed) I just ran:

sudo easy_install lxml

For Ubuntu you have to take a few other steps because you need a few dependencies and the development headers for Python.

If you don’t have setuptools installed:

sudo apt-get install python-setuptools

Then you need to apt-get install the following if you do not have them installed:

After that you can go ahead and:

sudo easy_install lxml

If you have build problems you probably don’t have the build tools installed:

sudo apt-get install build-essential

Then run easy_install again.

If you decide not to run lxml or do not have the ability to install it, the tool will still run you just won’t be able to use the Fixation handler without a nice failure and error message :)

Payload Types

There are several types of payloads you can construct with MonkeyFist. Each of these would depend on what the goal of the attack would be or the type of content on a site you would have control over. The basic payload types are dynamic redirect, POST construct, dynamic page, and fixation.

Dynamic Redirect

The dynamic redirect payload simply parses any cross-domain information looking for session data to dynamically construct in to a GET based payload to send back to the user’s browser. Basically, the user would request something and the tool would respond with a 302 redirect to a location. The location value would be the constructed payload. The user’s browser would just request content like normal and follow the redirect and execute the payload.

This payload type is best used in instances where you have the ability to add images tags or other HTML to a site. This way it could be relatively hidden from a user’s browser.

Dynamic Page

This payload constructs a page that performs several functions depending on what type of attack you are performing. You can either have the page perform a GET or a POST for an attack. Both the GET and POST types will be submitted by the user’s browser. So what does the page do? The attack that you construct gets embedded in the page and after the attack happens the user is immediately redirected to a location of your choice. So you could perform an attack and immediately send someone to the Benny Lava video ;) This could be combined with an URL shortener for further obfuscation.

This payload is best used in instances where you have the ability to embed hyperlinks to pages. Another thing to note about the dynamic page payload is that it makes POST based CSRF a whole lot easier to pull off. If you thought submitted data as a POST was a protection mechanism for CSRF you might want to rethink you point of view ;)

POST Construct

This payload is a bit different because the POST request is made by the tool and not the user’s browser. This needs to be kept in mind when using it. You will not have the advantage of the browser being helpful and submitting header information. If the cross-domain leakage is enough that you can perform an entire POST request without the user’s browser then this payload can be used. Otherwise, it will be pretty useless to you :)


The fixation payload allows you to make a request for data that you fixate on to the attack you send to the user. This is still experimental and only works in some narrow situations. This will be expanded later. This works as a modified page payload that performs and extra request and parses the response and gains the necessary information to perform the attack. This would be commonly used to make a request for tokens that you can fixate on to a request forged by the user’s browser.

Default Payload

The default payload gets matched when there is no cross-domain information for the tool to match with your entries in the payloads.xml file. It’s best to not perform an attack with this ;) The best thing to do is to make this a link to some real content like an image. This can make the tool a bit more stealthy.

You need to specify a default payload. Not doing so would be like crossing the streams. Well maybe not that bad, but it wouldn’t be good.

MonkeyFist Running Options

There are only a couple of running options with MF and well, all of them do not work as of yet. So, the main one you need to be familiar with is -s. This is the standard attack mode. The -p option specifies the port you would like MF to run on. You won’t need privileged access unless you are trying to run on a low order port. The following would run MonkeyFist on port 8080 using standard attack mode:

./MonkeyFist -p 8080 -s

You can get the about information by running -a, just in case you were curious about what version you are running.

./MonkeyFist -a

Of course, if you need some reference there is always the ole’ help with -h

./MonkeyFist -h

There are a couple of other options that are planned for the future. A testing mode and a random mode will be added as well, but currently, they are not implemented.


The payloads.xml file is where you define your attacks. This is where all of your work will be done. The exact options that are specified in this file are still being worked out. This is because as content goes, there needs to be flexibility when identifying these issues. There is a basic set of options that allow you to pull of some attacks even as MonkeyFist sits at version 0.4. Expect some changes in these options. The payloads.xml file will be covered in more detail in a future post.

The Others

You will notice a few other files in the MonkeyFist zip file. You might not want to delete them or you may have some unintended consequences. The page2.html file is blank, but it won’t be if you pull off any Page attacks. Contents are put in to this file dynamically and change per attack. is something I didn’t write, it just allowed me to quickly generate some HTML. This was before I made the decision to use lxml. For now I am going to leave it in there, even though it is not the best option. is the most important. This is the workhorse that takes care of all the work.

In Closing

I think that’s it for a small intro on MonkeyFist. In future posts I will explain more about the payloads and how they are constructed. If you notice any problems while running MF please let me know. You can send an email to monkeyfist {at} hexsec {dot} com. This is still a work in progress so please don’t beat me up too bad. I do welcome your feedback though. Thanks.

Share with your friends!
  • Facebook
  • Twitter
  • Google Plus
  • LinkedIn
  • StumbleUpon
  • Add to favorites
  • Email
  • RSS

Comments are closed.