Summary

Web fuzzing is a critical technique that every penetration tester should master. Unlike traditional methods that rely on predictable inputs, fuzzing systematically explores the vast input space to uncover hidden vulnerabilities, often revealing weaknesses that would otherwise remain unnoticed.

In this module, you will learn how to effectively use fuzzing tools to discover hidden directories, files, and parameters within web applications. This knowledge will enable you to uncover vulnerabilities and strengthen the security posture of your target web applications.

In this module, we will cover:

The fundamentals of web fuzzing and its significance
Techniques for directory and file fuzzing
Methods for parameter and value fuzzing
Analyzing and filtering fuzzing results
Validating and responsibly disclosing findings
Understanding WebAPI's and fuzzing them

This module is broken down into sections with accompanying hands-on exercises to practice each of the tactics and techniques we cover. The module ends with a practical hands-on skills assessment to gauge your understanding of the various topic areas.

As you work through the module, you will see example commands and command output for the various topics introduced. It is worth reproducing as many of these examples as possible to reinforce further the concepts introduced in each section. You can do this in the target host provided in the interactive sections or your own virtual machine.

You can start and stop the module at any time and pick up where you left off. There is no time limit or "grading," but you must complete all of the exercises and the skills assessment to receive the maximum number of cubes and have this module marked as complete in any paths you have chosen.

The module is classified as "Easy" but assumes a working knowledge of the Linux command line and an understanding of information security fundamentals.

A firm grasp of the following modules can be considered prerequisites for successful completion of this module:

Introduction to Networking
Linux Fundamentals
Web Requests

Introduction

Web fuzzing is a critical technique in web application security to identify vulnerabilities by testing various inputs. It involves automated testing of web applications by providing unexpected or random data to detect potential flaws that attackers could exploit.

In the world of web application security, the terms "fuzzing" and "brute-forcing" are often used interchangeably, and for beginners, it's perfectly fine to consider them as similar techniques. However, there are some subtle distinctions between the two:

Fuzzing vs. Brute-forcing

Fuzzing casts a wider net. It involves feeding the web application with unexpected inputs, including malformed data, invalid characters, and nonsensical combinations. The goal is to see how the application reacts to these strange inputs and uncover potential vulnerabilities in handling unexpected data. Fuzzing tools often leverage wordlists containing common patterns, mutations of existing parameters, or even random character sequences to generate a diverse set of payloads.
Brute-forcing, on the other hand, is a more targeted approach. It focuses on systematically trying out many possibilities for a specific value, such as a password or an ID number. Brute-forcing tools typically rely on predefined lists or dictionaries (like password dictionaries) to guess the correct value through trial and error.

Here's an analogy to illustrate the difference: Imagine you're trying to open a locked door. Fuzzing would be like throwing everything you can find at the door - keys, screwdrivers, even a rubber duck - to see if anything unlocks it. Brute-forcing would be like trying every combination on a key ring until you find the one that opens the door.

Why Fuzz Web Applications?

Web applications have become the backbone of modern businesses and communication, handling vast amounts of sensitive data and enabling critical online interactions. However, their complexity and interconnectedness also make them prime targets for cyberattacks. Manual testing, while essential, can only go so far in identifying vulnerabilities. Here's where web fuzzing shines:

Uncovering Hidden Vulnerabilities: Fuzzing can uncover vulnerabilities that traditional security testing methods might miss. By bombarding a web application with unexpected and invalid inputs, fuzzing can trigger unexpected behaviors that reveal hidden flaws in the code.
Automating Security Testing: Fuzzing automates generating and sending test inputs, saving valuable time and resources. This allows security teams to focus on analyzing results and addressing the vulnerabilities found.
Simulating Real-World Attacks: Fuzzers can mimic attackers' techniques, helping you identify weaknesses before malicious actors exploit them. This proactive approach can significantly reduce the risk of a successful attack.
Strengthening Input Validation: Fuzzing helps identify weaknesses in input validation mechanisms, which are crucial for preventing common vulnerabilities like SQL injection and cross-site scripting (XSS).
Improving Code Quality: Fuzzing improves overall code quality by uncovering bugs and errors. Developers can use the feedback from fuzzing to write more robust and secure code.
Continuous Security: Fuzzing can be integrated into the software development lifecycle (SDLC) as part of continuous integration and continuous deployment (CI/CD) pipelines, ensuring that security testing is performed regularly and vulnerabilities are caught early in the development process.

In a nutshell, web fuzzing is an indispensable tool in the arsenal of any security professional. By proactively identifying and addressing vulnerabilities through fuzzing, you can significantly enhance the security of your web applications and protect them from potential threats.

Essential Concepts

Before we dive into the practical aspects of web fuzzing, it's important to understand some key concepts:

Concept	Description	Example
`Wordlist`	A dictionary or list of words, phrases, file names, directory names, or parameter values used as input during fuzzing.	Generic: `admin`, `login`, `password`, `backup`, `config` Application-specific: `productID`, `addToCart`, `checkout`
`Payload`	The actual data sent to the web application during fuzzing. Can be a simple string, numerical value, or complex data structure.	`' OR 1=1 --` (for SQL injection)
`Response Analysis`	Examining the web application's responses (e.g., response codes, error messages) to the fuzzer's payloads to identify anomalies that might indicate vulnerabilities.	Normal: 200 OK Error (potential SQLi): 500 Internal Server Error with a database error message
`Fuzzer`	A software tool that automates generating and sending payloads to a web application and analyzing the responses.	`ffuf`, `wfuzz`, `Burp Suite Intruder`
`False Positive`	A result that is incorrectly identified as a vulnerability by the fuzzer.	A 404 Not Found error for a non-existent directory.
`False Negative`	A vulnerability that exists in the web application but is not detected by the fuzzer.	A subtle logic flaw in a payment processing function.
`Fuzzing Scope`	The specific parts of the web application that you are targeting with your fuzzing efforts.	Only fuzzing the login page or focusing on a particular API endpoint.

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Relevant Paths

This module progresses you towards the following Paths

Web Penetration Tester

The Web Penetration Tester Job Role Path is for individuals who want to enter the world of web penetration testing with little to no prior experience in it. This path covers core web security assessment and web penetration testing concepts, and provides a deep understanding of the attack tactics used during web penetration testing. Armed with the necessary theoretical background, multiple practical exercises, and a proven web penetration testing methodology, students will go through all web penetration testing stages, from reconnaissance and vulnerability identification to exploitation, documentation, and communication to vendors. Upon completing this job role path, you will have become proficient in the most common web penetration testing and attack techniques against web applications and APIs, and be in the position of professionally reporting vulnerabilities to a vendor.

Medium

279 Sections

Required: 1410

Reward: +330

20 Modules included

Web Requests

Fundamental

8 Sections

Reward: +10

This module introduces the topic of HTTP web requests and how different web applications utilize them to communicate with their backends.

Introduction to Web Applications

Fundamental

17 Sections

Reward: +10

In the Introduction to Web Applications module, you will learn all of the basics of how web applications work and begin to look at them from an information security perspective.

Using Web Proxies

Easy

15 Sections

Reward: +20

Web application penetration testing frameworks are an essential part of any web penetration test. This module will teach you two of the best frameworks: Burp Suite and OWASP ZAP.

Information Gathering - Web Edition

Easy

19 Sections

Reward: +20

This module equips learners with essential web reconnaissance skills, crucial for ethical hacking and penetration testing. It explores both active and passive techniques, including DNS enumeration, web crawling, analysis of web archives and HTTP headers, and fingerprinting web technologies.

Web Fuzzing

Easy

12 Sections

Reward: +10

In this module, we explore the essential techniques and tools for fuzzing web applications, an essential practice in cybersecurity for identifying hidden vulnerabilities and strengthening web application security.

JavaScript Deobfuscation

Easy

11 Sections

Reward: +10

This module will take you step-by-step through the fundamentals of JavaScript Deobfuscation until you can deobfuscate basic JavaScript code and understand its purpose.

Cross-Site Scripting (XSS)

Easy

10 Sections

Reward: +20

Cross-Site Scripting (XSS) vulnerabilities are among the most common web application vulnerabilities. An XSS vulnerability may allow an attacker to execute arbitrary JavaScript code within the target's browser and result in complete web application compromise if chained together with other vulnerabilities. This module will teach you how to identify XSS vulnerabilities and exploit them.

SQL Injection Fundamentals

Medium

17 Sections

Reward: +10

Databases are an important part of web application infrastructure and SQL (Structured Query Language) to store, retrieve, and manipulate information stored in them. SQL injection is a code injection technique used to take advantage of coding vulnerabilities and inject SQL queries via an application to bypass authentication, retrieve data from the back-end database, or achieve code execution on the underlying server.

SQLMap Essentials

Easy

11 Sections

Reward: +20

The SQLMap Essentials module will teach you the basics of using SQLMap to discover various types of SQL Injection vulnerabilities, all the way to the advanced enumeration of databases to retrieve all data of interest.

Command Injections

Medium

12 Sections

Reward: +20

Command injection vulnerabilities can be leveraged to compromise a hosting server and its entire network. This module will teach you how to identify and exploit command injection vulnerabilities and how to use various filter bypassing techniques to avoid security mitigations.

File Upload Attacks

Medium

11 Sections

Reward: +20

Arbitrary file uploads are among the most critical web vulnerabilities. These flaws enable attackers to upload malicious files, execute arbitrary commands on the back-end server, and even take control over the entire server and all web applications hosted on it and potentially gain access to sensitive data or cause a service disruption.

Server-side Attacks

Medium

19 Sections

Reward: +20

A backend that handles user-supplied input insecurely can lead to devastating security vulnerabilities such as sensitive information disclosure and remote code execution. This module covers how to identify and exploit server-side bugs, including Server-Side Request Forgery (SSRF), Server-Side Template Injection (SSTI), and Server-Side Includes (SSI) injection attacks.

Easy

13 Sections

Reward: +20

The module contains an exploration of brute-forcing techniques, including the use of tools like Hydra and Medusa, and the importance of strong password practices. It covers various attack scenarios, such as targeting SSH, FTP, and web login forms.

Broken Authentication

Medium

14 Sections

Reward: +20

Authentication is probably the most straightforward and prevalent measure used to secure access to resources, and it's the first line of defense against unauthorized access. Broken authentication is listed as #7 on the 2021 OWASP Top 10 Web Application Security Risks, falling under the broader category of Identification and Authentication failures. A vulnerability or misconfiguration at the authentication stage can impact an application's overall security.

Web Attacks

Medium

18 Sections

Reward: +20

This module covers three common web vulnerabilities, HTTP Verb Tampering, IDOR, and XXE, each of which can have a significant impact on a company's systems. We will cover how to identify, exploit, and prevent each of them through various methods.

File Inclusion

Medium

11 Sections

Reward: +10

File Inclusion is a common web application vulnerability, which can be easily overlooked as part of a web application's functionality.

Attacking GraphQL

Mini-Module

Medium

9 Sections

Reward: +20

GraphQL is a query language for APIs as an alternative to REST APIs. Clients are able to request data through GraphQL queries. If improperly configured or implemented, common web security vulnerabilities such as Information Disclosure, SQL Injection, and Insecure Direct Object Reference (IDOR) may arise.

API Attacks

Medium

13 Sections

Reward: +20

Web APIs serve as crucial connectors across diverse entities in the modern digital landscape. However, their extensive functionality also exposes them to a range of potential attacks. This module introduces API Attacks, with a specific focus on the OWASP API Security Top 10 - 2023.

Attacking Common Applications

Medium

33 Sections

Reward: +20

Penetration Testers can come across various applications, such as Content Management Systems, custom web applications, internal portals used by developers and sysadmins, and more. It's common to find the same applications across many different environments. While an application may not be vulnerable in one environment, it may be misconfigured or unpatched in the next. It is important as an assessor to have a firm grasp of enumerating and attacking the common applications discussed in this module. This knowledge will help when encountering other types of applications during assessments.

Bug Bounty Hunting Process

Easy

6 Sections

Reward: +10

Bug bounty programs encourage security researchers to identify bugs and submit vulnerability reports. Getting into the world of bug bounty hunting without any prior experience can be a daunting task, though. This module covers the bug bounty hunting process to help you start bug bounty hunting in an organized and well-structured way. It's all about effectiveness and professionally communicating your findings.