Fuzzing: What Is It and How to Protect Yourself from It?

The pressure is on to test your software!

If you’re a developer, you’ve likely encountered serious bugs that ruined your code. As a result, you should adopt a testing approach before releasing, and fuzzing is one of these testing techniques. It’s a process where you enter known data into a system to see if the result produced is as expected. Software developers use this process to test systems for bugs that cybercriminals could exploit later.

In this article, you’ll learn what fuzzing is, how it works, and how you can implement it into your coding. First, let’s take a look at what fuzzing is!

What Is Fuzzing?

Fuzz testing is a process that allows both software developers and cybercriminals to check a program or system for an exploitable bug. To understand fuzzing, you can think of a black box diagram. An input will go through a maze hidden in the box, and a solution will come out of the other end. 

You can break down your program into many functions and logical processes. Each one also can have its own black body diagrams. If you know the software, you should be able to map it out on paper. After that, you can understand what should happen with each input.

However, inputs don’t always yield the desired results. In fact, a program can have many flaws, the programmer may even have missed something. Additionally, the program’s interactions with its environment can create a flaw. Even simple programs can be flawed

This testing process has been around since 1988. Originally, it aimed to test the reliability of operating systems at the University of Wisconsin by feeding them random inputs. Unfortunately, when tested, these random inputs crashed the university’s systems around a third of the time

After seeing these numerous crashes, the tech industry started paying more attention to testing software. This way, cybercriminals wouldn’t discover exploits as easily, and software wouldn’t crash in the wild. 

With all that being said, we can further dive into the different generations of fuzzing methods. This will help you understand how fuzz testing actually works. 

How Does Fuzzing Work?

Over time, fuzzing has evolved into 3 distinct generations. Each generation is also an improvement over the other. Let’s go through each generation. 

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Shift your gears, find your bugs!

Generation 1: Random Fuzzing

Random fuzzing was the original technique. It simply fed randomized data into the program and looked for unexpected results. For instance, say you input 2+2 into a calculator and are given 5 as the answer. Clearly, the answer shouldn’t be 5, but this error could occur for a number of reasons, even for basic calculator programs. For instance, you could be using float variables instead of integers.  

Generation 2: Grammar-Based Fuzzing

Grammar-based fuzzing is where the input data going into the program is constructed using rules. Many different fuzzing software on the market currently uses this process. Grammar-based fuzzing only logically goes through every route once, unlike random fuzzing. But if the logic for the rules is too constraining, you may miss large parts of the program.

Generation 3: Instrument-Guided Fuzzing

Instrument-guided fuzzing is also called artificial intelligence (AI)-guided fuzzing. This method uses a monitoring utility to record where each probe has gone and also ensures routes aren’t repeated. Sure, you don’t really need to use AI. But this choice is becoming popular as it makes the process more efficient. Companies like Google are using this third-generation process to test software they’re developing. Unlike grammar-based or random fuzzing, instrument-guided fuzzing has fewer chances to miss routes in the software.  

How Cybercriminals Use Fuzzing

Cybercriminals use fuzzing to find a weakness in a program. For websites, this could be through entering random characters into a page extension to find an SQL database exploit. In fact, this is a common process used by penetration testers. It helps them assess security threats or exploit rewards from the company. Most companies have some form of zero-day exploit rewards, which makes the process competitive between testers. Additionally, penetration testers often use web-scraping tools at this stage. This way, they get information to add to their fuzzing queries.

The National Security Agency (NSA) uses a form of fuzzing in a program they developed called Chimera. This software has been around for a while. It can take programs that have been compiled into an ‘unreadable’ construction language. Then, it reverse engineers them. Many different parties–including cybercriminals–know about this software. As a result, the NSA released it on its website to help penetration testers

Cybercriminals can use this technique in many other ways. But fundamentally, they aim to find bugs that they can leverage. Where possible, cybercriminals will also use the third generation of fuzzing in their exploits. Automating the process and using a mapping feature can drastically reduce the time or computation required to find a useful exploit.   

How to Protect Yourself From Fuzzing

Fuzz testing can be a big problem depending on the attack surface. For websites, you can add a timeout or delay to queries. This will stop automated tools from crashing the platform. Often, you also can use a Demilitarized zone (DMZ) to keep core business information separate from direct business-level database querying. Even if cybercriminals gain access to the DMZ, they’ll need to battle a zero-trust zone to gain access to the company’s internal workings.

Final Thoughts

Whenever you develop a piece of software, you must test it for bugs–ideally, using a third-generation solution. It’ll provide the most efficient and pragmatic approach to bug finding

Whether your software is a web application, or constructed in an automated building solution, you must test it. This is important to ensure you don’t have to write excessive numbers of patches once you release the software. Additionally, if you use SCRUM and release incrementally, you still need to test at each stage.

Do you have more questions about fuzzing methods? Check out the FAQ and Resources sections below!


What is fuzzing?

Software developers and cybercriminals use fuzzing to check a program or system for an exploitable bug. To understand this, you can think of a program as a black box diagram. Basically, an input will go through a maze hidden in the box, and a solution comes out the other side.

Which is the best fuzzing method to use?

If possible, use the latest third generation method called instrument-guided fuzzing. This method doesn’t have the problem of going down the same path multiple times like random fuzzing. It also won’t miss entire parts of the program due to flawed rules.

What is random fuzzing?

Random fuzzing is the process of testing software by entering random data into the system. Then, you’ll see what input will break it or cause an error. It’s great for validating the logic and security of a program. However, this process can allow the same routes to be tested repeatedly, meaning it’s not an efficient method. 

What is grammar-based fuzzing?

Grammar-based fuzzing defines rules  to help ensure routes tested aren’t repeated, unlike random fuzzing. However, if the rules are too strict or flawed, then large parts of the program could be skipped. If you want to use fuzz testing to test the software’s reliability, you’re better off using instrument-guided fuzzing.  

What is instrument-guided fuzzing?

Instrument-guided fuzzing effectively monitors and maps input routes during the process. This stops routes from being repeatedly tested. Therefore, it’s very effective and helps ensure you don’t miss parts of the software. Instrument-guided fuzzing is the latest and best method to fuzz your software.


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