OWASP JBroFuzz Tutorial

JBroFuzz Tutorial

Introduction

“If you can’t fuzz with JBroFuzz, you probably do not want to fuzz!” JBroFuzz Motto

The art of teaching, Mark Van Doren said, is the art of assisting discovery. Fuzzing is a representative discipline towards assisting the discovery of security vulnerabilities that is just beginning to come of age. Over the last two years, through continuous development, JBroFuzz has attempted to expose the intrinsic beauty of the subject: Constantly submit a vast amount of payloads to a service, device or prompt, waiting for the one response that makes all the difference. This is the mentality that JBroFuzz embraces and attempts to offer back to security professionals.

Fuzzing as a concept goes beyond a conventional workflow or a standard methodology. I would argue that to know how to fuzz well, is to master a new language. Thus, similar to the process of learning a programming (or foreign) language, there are three things you must master:

• Grammar: How fuzzing as a process is structured
• Vocabulary: How to name fuzzing concepts you want to use
• Usage: Ways of achieving everyday effective results with fuzzing

From the pre-existing information available for JBroFuzz, this tutorial focuses on usage: How to best put a fuzzing tool to good use, either via the UI, or using APIs that JBroFuzz.jar is constituted of. As a result, this document has a small requirement as a caveat; you need to have a beginner level understanding of the Java programming language in order to understand some sections.

There are a number of working examples described here within, which grep for statements such as “public static void main(String[] args)”. The majority of the content relates to reviewing these examples and putting the Java syntax into a fuzzing perspective.

To summarise, this tutorial focuses on customary and effective usage of fuzzing through the JBroFuzz Java APIs and the respective UI. It is targeting (without attacking them) web applications. Without further redo, let’s get fuzzing!

'Hello Google!' (forget 'Hello World')

As the traditional first program that you learn when indulging in a new programming language, 'Hello World!' represents the norm for understanding the basic output operations and syntax (let alone compiler and execution behaviour) of the language in question.

As with most security tools, when I am given the responsibility to run them, often to understand how they work, I would first craft a legitimate, single request to a trusted (to be up and behaving) popular Internet location. Needless, to say this request more than on occasion finds itself on Google servers.

So 'Hello World!' for programming languages seems to transform to 'Hello Google!' for understanding how security tools work. Let us see, how JBroFuzz does it.

• Double-click on JBroFuzz and browse to the 'Fuzzing' tab (typically bottom left)
• In the 'URL' field type: http://www.google.com
• In the 'Request' field type: GET / HTTP/1.0 and press 'Enter' twice
• Hit 'Start' or Ctrl+Enter

You should see a response received in the bottom part of the 'Fuzzing' panel. Double click (or right click for more options) to see the information exchanged; typically this would be a 302 redirect pointing you to another location. Congratulations, you have just said "Hello" to Google!

Now this would typically be enough under RFC rules, to get a response back; but damn all the bots outhere, most websites require further information to respond back. So, in the 'Request' field let's pretend to be a (kind of) legitimate browser by typing:

GET / HTTP/1.0
Host: www.google.com
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.9.0.10) Gecko/2009042316 Firefox/3.0.10 (.NET CLR 3.5.30729) JBroFuzz/1.5
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-gb,en;q=0.5
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7


Not forgetting to end the request typed with two returns: Press 'Enter' twice. Again, you should be able to see a line added with the response received back.

Practice sending single requests to a website of your choice by changing the URL and also the 'Host:' field from the 'Request' above. Also try accessing an https website.

Alternatively, you can use the shortcut Ctrl+L to type in your URL, with the 'Request' field filled automatically, based on the URL you have typed.