Web ApplicationJuly 20, 2023Mastering Burp Suite Extension Development 

Burp Suite, developed by PortSwigger, is a powerful web application security testing tool widely used by security professionals and penetration testers. It offers a comprehensive set of features and functionalities, making it an indispensable tool for identifying vulnerabilities and securing web applications. 

In this blog, we will focus on understanding the basics of the Burp Suite before diving into burp suite extension development. Burp Suite consists of several modules, including a proxy, scanner, intruder, repeater, and sequencer, each serving a specific purpose in the testing process. The tool provides an intuitive user interface and allows users to interact with web applications, intercept and modify HTTP requests and responses, and analyze the security posture of the target application. 

Why develop extensions for Burp Suite? 

While the built-in features of Burp Suite are incredibly powerful, they may not always cater to the specific needs of every security professional. This is where Burp Suite extension development comes into play. By developing extensions, you can extend the functionality of Burp Suite to meet your unique requirements and enhance your testing capabilities. 

Developing extensions for Burp Suite provides flexibility and customization options. You can add new features, automate repetitive tasks, integrate external tools, and create new modules within Burp Suite. This level of customization empowers security professionals to tailor Burp Suite to their specific workflow and maximize their efficiency in conducting web application security assessments. 

Getting Started with Burp Suite Extension Development 

Before you start developing Burp Suite extensions, setting up your development environment is crucial. You will need Java Development Kit (JDK), an Integrated Development Environment (IDE), and the Burp Suite Extender API. 

First, install the latest version of JDK and set up the environment variables. Next, choose an IDE that suits your preferences and configure it for Java development. Popular choices include Eclipse, IntelliJ IDEA, and NetBeans. 

Once your development environment is set up, you need to obtain the Burp Suite Extender API. This API provides developers with comprehensive classes and methods to interact with Burp Suite. You can download the Burp Suite Extender API from the PortSwigger website and add it to your project’s classpath. 

Anatomy of a Burp Suite Extension 

To understand how to develop Burp Suite extensions, it is essential to grasp an extension’s basic structure and components. A Burp Suite extension is a Java class that implements the IBurpExtender interface. This interface defines the methods that Burp Suite invokes during the extension lifecycle. 

The extension class should be packaged as a JAR file and loaded into Burp Suite using the Extender tab. Once loaded, Burp Suite initializes the extension by invoking the registerExtenderCallbacks method, where you can register your custom callbacks and modify the behavior of Burp Suite. 

In addition to the IBurpExtender interface, Burp Suite provides several other interfaces that you can implement to extend specific functionalities. These interfaces include IProxyListener, IScannerCheck, IIntruderPayloadGenerator, and many more. By implementing these interfaces, you can hook into different modules of Burp Suite and customize their behavior. 

Key Features and Functionalities

Burp Suite extensions offer many features and functionalities that can significantly enhance your web application security testing process. Here are some key features and functionalities you can develop using Burp Suite extensions: 

  1. Customized scanning checks: By implementing the IScannerCheck interface, you can create custom scanning checks to identify specific vulnerabilities in web applications. This allows you to extend Burp Suite’s built-in scanner and tailor it to your testing requirements. 
  2. Workflow automation: Burp Suite extensions enable you to automate repetitive tasks and streamline your testing workflow. You can create custom macros, scripts, or plugins to perform common actions automatically, saving you time and effort. 
  3. Integration with external tools: Burp Suite extensions provide the ability to integrate with external tools and services. You can leverage APIs and libraries to interact with other security tools, vulnerability scanners, or data analysis platforms, enabling you to leverage the power of multiple tools within a single testing environment. 
  4. Reporting and visualization: With Burp Suite extensions, you can generate customized reports and visualizations to present your findings clearly and concisely. You can export scan results, vulnerabilities, and other data into various formats, such as HTML, PDF, or CSV, and create interactive dashboards for better data analysis. 

Developing your first Burp Suite extension – a step-by-step guide 

Now that you understand Burp Suite extension development well let’s walk through the process of developing your first one. This step-by-step guide will help you get started and familiarize yourself with the key concepts and techniques involved in extension development. 

Step 1: Define the requirements 

Before diving into coding, it is crucial to define the requirements of your extension. Identify the problem you are trying to solve or the functionality you want to add to Burp Suite. This will help you stay focused and ensure your extension meets the desired objectives. 

Step 2: Set up the development environment 

As mentioned, set up your development environment by installing the JDK, configuring your IDE, and obtaining the Burp Suite Extender API. Make sure all the necessary dependencies are in place before starting to code. 

Step 3: Create the extension class 

Create a new Java class that implements the IBurpExtender interface. This class will serve as the entry point for your extension. Override the registerExtenderCallbacks method and add your custom logic inside it. 

Step 4: Implement the desired functionality 

Implement the desired functionality by leveraging the various interfaces provided by Burp Suite. For example, to create a custom scanning check, implement the IScannerCheck interface and define your check logic in the doActiveScan or doPassiveScan method. 

Step 5: Test and debug your extension 

Testing and debugging your extension is crucial to ensure its reliability and correctness. Use the built-in testing capabilities of Burp Suite to validate your extension’s functionality and identify any issues or bugs. Leverage the debugging tools provided by your IDE to step through your code and inspect variables. 

Step 6: Package and distribute your extension 

Once you are satisfied with the functionality and stability of your extension, package it as a JAR file. Make sure to include any necessary dependencies and resources. You can then distribute your extension to other security professionals or the wider community, allowing them to benefit from your work. 

Advanced Techniques and best practices 

To take your Burp Suite extension development skills to the next level, exploring advanced techniques and following best practices is essential. Here are some tips and recommendations to help you build robust and efficient Burp Suite extensions: 

  1. Optimize performance: Optimize your extension by minimizing resource usage and avoiding unnecessary computations. This will help prevent any negative impact on the overall performance of Burp Suite. 
  2. Handle errors gracefully: Implement proper error handling for exceptions and unexpected scenarios. Graceful error handling will enhance the stability and reliability of your extension. 
  3. Secure sensitive information: Be cautious when handling sensitive information, such as authentication credentials or API keys. Encrypt or obfuscate sensitive data to prevent unauthorized access or misuse. 
  4. Leverage multithreading: Utilize multithreading techniques to improve the responsiveness and efficiency of your extension. Offload time-consuming tasks to separate threads to prevent blocking the main Burp Suite process. 
  5. Follow coding best practices: Adhere to coding best practices, such as using meaningful variable and method names, writing modular and reusable code, and documenting your code effectively. This will make your extension more maintainable and easier to understand for yourself and other developers. 

Building a Burp Suite Extension 

To illustrate the concepts discussed, let’s walk through a sample code walkthrough of building a Burp Suite extension.  

Step 1: Set up the development environment 

To create a Burp Suite plugin, you’ll need to have the following set up: 

  • JDK (Java Development Kit) installed 
  • Burp Suite Professional edition (available from PortSwigger’s website) 
  • A Java IDE (e.g., IntelliJ IDEA, Eclipse, or Visual Studio Code) 
Step 2: Create a new Java project 

Start by creating a new Java project in your IDE. 

Step 3: Add Burp Suite’s Extender API to the project 

In your IDE, add the Burp Suite Extender API JAR file to your project’s build path. The JAR file is typically named “burp-extender-api.jar” and can be found in the “Burp Suite” installation directory. 

Step 4: Implement the Burp Suite plugin 

Here’s a simple Burp Suite plugin that logs HTTP responses to the output console: 

import burp.*; 

public class BurpLogger implements IHttpListener { 

   private IBurpExtenderCallbacks callbacks; 

   public BurpLogger(IBurpExtenderCallbacks callbacks) { 

       this.callbacks = callbacks; 
       this.callbacks.setExtensionName("Burp Logger"); 


  public void processHttpMessage(int toolFlag, boolean messageIsRequest, IHttpRequestResponse messageInfo) { 

       if (!messageIsRequest) { 

           // Get the response details 
           IResponseInfo responseInfo = this.callbacks.getHelpers().analyzeResponse(messageInfo.getResponse()); 
           int statusCode = responseInfo.getStatusCode(); 
           String statusText = responseInfo.getStatusText(); 
           String responseBody = new String(messageInfo.getResponse()); 

            // Log the response details to the output console 
           this.callbacks.printOutput("Received Response: " + statusCode + " " + statusText); 
           this.callbacks.printOutput("Response Body:\n" + responseBody + "\n\n"); 

Step 5: Register the plugin with Burp Suite 

Next, you need to register your plugin with Burp Suite: 

public class BurpExtender implements IBurpExtender { 

   public void registerExtenderCallbacks(IBurpExtenderCallbacks callbacks) { 

       // Instantiate the BurpLogger and register it as an HTTP listener 
       BurpLogger burpLogger = new BurpLogger(callbacks); 

       // Perform any additional setup if needed 

Step 6: Build and load the plugin 

Build the Java project to create a JAR file for your Burp Suite plugin. Then, in Burp Suite, go to “Extender” > “Extensions” > “Add” to load your plugin’s JAR file. 

Step 7: Test the plugin 

Once the plugin is loaded, use Burp Suite as usual, and the responses will be logged to the output console. 

Please note that this is a basic example, and Burp Suite provides an extensive API to perform various tasks, such as modifying requests/responses, adding custom scanner checks, or implementing active/passive checks. You can explore the Burp Suite Extender API documentation for more details on available interfaces and methods:  

Also, ensure that you understand the potential security implications of using a custom Burp Suite plugin and test it thoroughly in controlled environments before using it in production or on sensitive systems. 

Resources and Tools 

As you embark on your journey to master Burp Suite extension development, here are some valuable resources and tools that can assist you: 

  1. PortSwigger’s Burp Suite Extender API documentation: The official documentation provided by PortSwigger is an invaluable resource for understanding the various classes, interfaces, and methods available for extension development. It provides detailed explanations, code examples, and usage guidelines. 
  2. Burp Suite community forums: The Burp Suite community forums are an excellent platform to seek guidance, ask questions, and share your experiences with other Burp Suite extension developers. The community is active and supportive, making it a valuable resource for troubleshooting and collaboration. 
  3. Open-source Burp Suite extensions: Explore open-source Burp Suite extensions available on platforms like GitHub. Analyzing the code of existing extensions can provide insights into best practices, design patterns, and advanced techniques experienced developers use. 
  4. Burp Suite plugin development libraries: Several third-party libraries are available that can simplify and accelerate the development of Burp Suite extensions. These libraries provide additional functionalities, utilities, and integrations that can enhance your extension development experience. 

Redfox Security is a diverse network of expert security consultants with a global mindset and a collaborative culture. If you are looking to improve your organization’s security posture, contact us today to discuss your security testing needs. Our team of security professionals can help you identify vulnerabilities and weaknesses in your systems, and provide recommendations to remediate them.

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Chirag Lundwani

by Chirag Lundwani

Security Consultant | Redfox Security