The Must-read Comprehensive Guide to Fuzz Testing

Fuzz Testing

A-Z About Fuzz Testing

We are all living in a technological world, a boon. However, the bane is Cyber Attacks. The security loopholes require testing to prevent system crashes. Hence, Barton Miller developed Fuzz Testing in 1989.

What is Fuzz Testing?

The coding error and the security loopholes are discovered by incorporating an invalid code or random data into the system. Then, you can test the system for cases like a failure in built-in code or system crashing by inserting the data using semi-automatic or automated techniques.

Nowadays, there are various options for a commercial tool that helps to incorporate fuzzing, as it requires lesser effort and is one of the most effective ways of testing applications.

Fuzz testing commonly known as fuzzing is an automated technique of software testing which helps in finding the security loopholes in the software by putting in data randomly. Then this data help in finding the security loopholes and coding errors.

Fuzz testing is a traditional yet common process used by defenders. It helps in finding and fixing the bugs or the hackers who seek vulnerability and find the bugs in the hackers’ software. 


Why do Fuzz Testing?

Some of the essential reasons why you should do fuzz testing on your system application are:

  • Helps tracking the most severe defect or security fault in the software or application
  • Gives the best results if used along with beta testing, blackbox testing, and other testing methods
  • Helps to check the susceptivity of the software
  • A very cost-effective method of testing
  • Helps in revealing the overlooked yet important and serious defects while debugging or writing the software. You can prevent such problems through fuzz testing. 

How to do Fuzz Testing?

The basic steps of the fuzz testing are:

  • Identifying the target system
  • Find the inputs
  • Create fuzz data
  • Incorporate( data) in the system
  • Execute the test using the data(fuzz)
  • Track the system defects
  • Log defects

Examples of Fuzzers:

The examples of fuzzer are:

Mutation-Based Fuzzers

In mutation-based testing, the tester alters the old data samples to create a new one. It starts with a sample of protocols that are valid and mangles every file or byte.

Generation-Based Fuzzers

In this, you need to generate the input from scratch according to the specification.

Protocol-Based Fuzzers

Keep a piece of detailed information ready about the protocol formats used for testing. Then, write the specification in the tool with the help of model-based testing generation techniques. Then add irregularity into sequence and data content. Hence, it is also called robustness testing, grammar testing, syntax testing. This type of testing can use invalid or valid inputs.


Types of bugs detected by Fuzz Testing

In large applications, the bugs affect the safety of memory. Hence, the methods essentially used are related to memory leak and assertion failures.

Invalid input

In this testing, invalid inputs are used to create invalid codes. This invalid input handles the error-handling routine and automates negative testing.

Correctness bugs

It detects correctness bugs, e.g., poor search results and corrupted databases.

Tools such as peach fuzz and burp suite are used in web security and fuzz testing.

Peach Fuzzer

Peach fuzz provides a more robust security cover. In addition, peach fuzz helps the user identify the unknown and known threads in the system while others only find the known threads.

Spike Proxy

Spike proxy looks for vulnerabilities at the application level in any web application. It is one of the most professional tools used for testing. Spike proxy takes care of the basics, e.g., cross-site scraping and SQL injection. It is available for both Windows and Linux.


Webscarab is written in Java which makes it portable to many devices. Communication in web scarab is done using HTTP, HTTPS protocols, and various applications are analyzed using it.

Suppose there are any loopholes in the system web carb finds and make a list of reported issues. It is an intercepting proxy. In this, the operator can review and modify the request before the server receives it. Similarly, it can be updated and checked before the browser gets it.

Advantages of Fuzz Testing

It has many advantages if used correctly; some of them are:

  • Improves the software security testing
  • Find severe bugs using fuzzing such as unhandled exception, crashes, memory leaks.
  • Helps in finding the bugs if failed to find due to time and resource constraints.

Disadvantages of Fuzz Testing

The disadvantages of this testing are:

  • It doesn’t give a complete picture of bugs or overall security threats
  • Detects only simple faults and threats
  • Requires significant amount of time to perform the test effectively
  • It is very problematic to set boundary value conditions for random inputs

Fuzz testing is ineffective for security threats that do not cause program crashes, e.g., worms, viruses, trojan, etc.


Let’s see some limitations of protocol base fuzzing:

  • The specification needs to be mature for testing through protocol-based fuzzing
  • Test coverage is limited for new protocols if the fuzz testing works on the principle of published specifications.

The best way to find bugs in the system is by sending random input into the system software. You can quickly conduct this test if the information is available by simply altering the information by inserting random data.