Fuzz Testing

Fuzz testing, which is a type of security testing, is used by software testers to find bugs and defects in the product, to validate its reliability and security. To define the significance of this testing, following is a detailed discussion on fuzz testing.

What is Fuzz Testing?

Originally developed in 1989 at the University of Wisconsin, by a professor named Barton Miller, fuzz testing or fuzzing is a software testing technique that helps the team of testers find security vulnerabilities in the software. Initially referred as random fuzzing, this testing is now used to discover serious security defects and errors.

Fuzz testing is a form of security & black box testing, where a tester tries to break into the system or web server with the help of random data values i.e. fuzz. In this methodology, generally coding errors & security vulnerabilities are explored by feeding invalid or random inputs to the system or software application. It may be seen as an automated or semi-automated process, where significant defects, mainly security gaps and crashes, potential memory leaks, etc. are revealed, so as to fix them.

Features of Fuzz Testing:

Fuzz testing is carried out with the objective of testing the system with the large quantity of corrupted data and to produce errors & defects, which are waiting to get discovered so that they may be corrected, accordingly. The other features and components that define fuzz testing and help in differentiating it from others are:

  • It is a security testing approach that helps find bugs in the software.
  • Fuzz testing or fuzzing tests the robustness of the interface robustness by stressing the interface of the system under test with invalid data inputs.
  • It helps find security relevant weakness and anomalies in the system.
  • It is an automated software testing technique, which uses fuzzers to implement random inputs in the program to detect defects.
  • The fuzzer can use existing test case or valid or invalid inputs.
  • It address various issues in the web application, such as crashes, memory leaks, buffer overflow, failing of built-in code assertions, or more.
  • It is most effective when used in conjunction with black box testing, beta testing, or other effective & efficient methods of debugging.

How to do Fuzz Testing?

As mentioned above, fuzzing follows an automated process, wherein it the testing can be automated to a high degree and results can be assessed and compared across various web applications, vendors, operating systems, and more. Moreover, the basic approach used to perform fuzz testing over a software product, consists of the following activities:

  • Identifying the target system.
  • Identifying the inputs.
  • Generating Fuzz Data.
  • Execution using Fuzz Data.
  • Observing the behaviour of the system.
  • Logging defects.

Furthermore, it may be performed either manually or with the assistance of various automated tools. However, it is preferable to approach automation for effective results.

Fuzz Testing Techniques:

This type of security testing may be carried out using any of the following methods:

  • Mutation based Fuzzers: This involves the alteration of the existing and available input data to generate the new test data.
  • Generation based Fuzzers: In this technique, new test data is designed & prepared based on the inputs of the model. Some of the examples of this model are GUI models, network protocols, file format, etc.
  • Protocol or Model based Fuzzers: It is an efficient technique, where new test data is being designed and prepared based on the knowledge of the protocol format to be tested. It generally, involves writing the specification in an array form into the tool and thereafter based on the specification, adding distortion or flaws in the input data, pattern, series, etc.

Types of defects, explored by Fuzzy Testing:

This testing technique is useful in discovering following types of defects:

  • Assertion Failure or Memory Leaks: Bugs or defects, which are responsible for hampering the safety of the memory.
  • Invalid Input: Defects arises from the invalid inputs, and are being responsible for the "error handling" feature of the software product.
  • Correctness Bug: It may include corrupted database, poor search results, etc.

Fuzz Testing Infographics:

Fuzz Testing Infographics

Advantages of Fuzz Testing:

Fuzz testing should be included in any comprehensive testing suite, as it offers the team a vast array of benefits, which help them validate the quality, effectiveness, as well as the security of the software. Hence, some of these advantages are:

  • Enhances the job of security testing.
  • Explore severe defects, which are left invisible, and could not be explored, even by the test cases designed and prepared, by an expert tester.
  • Ensure the coverage of all possible negative scenarios for the software product.
  • Detects race conditions and deadlocks and checks control flow integrity.

Disadvantages of Fuzz Testing

Apart from offering various benefits to the team of tester, developers, and end users, fuzzing also imparts few drawbacks, which needs acknowledgement. These disadvantages are:

  • Absence of proper planning, along with the non availability of specific exist criteria.
  • Requires significant amount of time, for its effective execution.
  • Alone, it is incapable to cover all possible security vulnerabilities and defects, present in the software product.

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Fuzz Testing Tools:

Nowadays, finding tools for the purpose of software testing has become extremely simple. The software industry is full of numerous high quality, open source, and agile tools that offer great assistance to testers. Hence, some of the popular tools, available in the market, for carrying out the task of fuzz testing, are:

  • Peach Fuzzing Platform: Helps protect software and hardware system by performing necessary security testing. Discover unknown vulnerabilities, using this automated, seamless, and scalable tool, and effortlessly secure your APIs.
  • Radamsa(a flock of fuzzers): An important fuzzer tool and test case generator that offers aid in robustness testing. Radamsa helps validate the strength of a program by providing malicious, malformed, and invalid inputs.
  • Microsoft SDL MiniFuzz File Fuzzer: This tools is fuzzer that is designed to identify defects and vulnerabilities in the software to enhance and validate its security. It exposes code flaws as well as unexpected and potentially anomalous behavior.
  • Untidy -XML Fuzzer: General purpose XML fuzzer, Untidy XML Fuzzer generates modified and invalid XMLs based on the inputs provided by the team earlier.
  • Burp:Burp is a security testing tool, used by Java based web applications. It supports platform authentication and detects various vulnerabilities like buffer overflow, SQL injection, cross-site scripting (XSS), etc.
  • Microsoft SDL Regex Fuzzer: This is an open source fuzzer, that helps the team in testing regular expressions for potential security vulnerabilities in the application’s code.
  • OWASPWSFuzzer: Written in Python, OWASP WSFuzzer targets web services. Created to automate real world manual SOAP pen testing work, it is a GPL’d program that cannot be replace manual human analysis.
  • ABNF Fuzzer.
  • The fuzzing mailing list.
  • Webscarab.


Fuzz testing or fuzzing can be termed as one of the crucial testing techniques performed to ensure the quality and reliability of a software product. The importance of this testing is such that it is executed by the team of testers in almost all comprehensive testing suites. Fuzzing aims to find all vulnerabilities and issues in the software that can impact its security and allows various threats to overcome a system. Hence, by implementing fuzz testing, one can guarantee the security of an application.

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