The art of fuzzing testing is an essential practice in any cybersecurity professional’s toolbox. Although the basis of this technique—supplying random inputs or “fuzz” to a system to identify errors—is simple, advanced applications of fuzzing can be complex and nuanced. In this article, we will explore advanced fuzzing techniques applied to JavaScript code and URLs, using the jsfuzz and wfuzz tools, respectively.

Fuzzing in JavaScript with jsfuzz

Step 1: jsfuzz configuration

Installation of jsfuzz is done through npm, using the npm install -g jsfuzz command. Make sure you have Node.js installed on your system before proceeding.

Step 2: Development of an advanced harness

Implementing a harness for jsfuzz should be more than just a function; It is necessary to consider different strategies to exert pressure on the various parts of the target code. For example, you could create a harness that explores the different ways to interact with an object in your code:

javascriptCopy code// harness.js const MyObject = require('./MyObject'); module.exports = { fuzz: function(data) { let obj = new MyObject(); data = new Uint8Array(data); let methodIndex = data[0] % 3; let arg = data[1]; switch(methodIndex) { case 0: obj.method1(arg); break; case 1: obj.method2(arg); break; case 2: obj.method3(arg); break; } } };

In this example, the harness attempts to call three different methods on an object with random arguments. Variety and randomness are keys to effective fuzzing.

Step 3: Execution and analysis

Runs jsfuzz at the command line, providing the location of the test code and initial test data. Analyze the results carefully, not only looking for errors but also observing unexpected behavior.

Fuzzing URLs with wfuzz

Step 1: Prepare wfuzz

You can install wfuzz using pip, the Python package manager. Use the command pip install wfuzz.

Step 2: Advanced fuzzing techniques

Next, we show you how to use wfuzz more effectively in URL fuzzing. You can apply multiple payloads and use custom filters and scripts to create more efficient fuzzing tests. Here we show you an advanced example of how to use wfuzz:

cssCopy codewfuzz -c -z file,wordlist1.txt -z file,wordlist2.txt --script=html --hc 404 http://example.com/FUZZ/FUZ2Z

In this example, we use two lists of words to apply more variations in the tests. --script=html tells wfuzz to use a custom script (in this case, a script that parses HTML) to parse the responses.

Despite its usefulness, remember that fuzzing is not a panacea. It will not detect all vulnerabilities and may lead to false positives. Therefore, you should combine fuzzing with other security testing techniques.

Additionally, it is crucial to obtain consent before performing security tests on third-party systems. Participating in bug bounty programs can be a great way to apply your fuzzing skills in an ethical and beneficial way.

Fuzzing as a Stage in the Continuous Integration and Delivery Process (CI/CD)

Incorporating fuzzing into the Continuous Integration and Delivery (CI/CD) pipeline can greatly strengthen the software development process. By doing so, security vulnerabilities and bugs can be automatically detected before the code reaches production.

Consider fuzzing as an automated testing stage in your CI/CD pipeline. After unit and integration testing, but before delivery or deployment, you can run your harness fuzzing. This could be as simple as a shell script that runs jsfuzz or wfuzz, or it could involve using a CI/CD tool that integrates fuzzing testing, such as Jenkins with its fuzzing plugin.

Additionally, continuous fuzzing also provides useful feedback to the development process, allowing developers to quickly see if a recent change has introduced new vulnerabilities.

Ultimately, incorporating fuzzing into your CI/CD pipeline enables a more proactive approach to security, making it easier to detect vulnerabilities early and helping to maintain the integrity of your code as it evolves and grows.