When developing applications, developers’ first priority is typically to make sure that the application is functioning as expected. So they primarily focus on handling expected inputs. In order to make the application robust, they also add mechanisms to handle invalid and unexpected inputs. However, sometimes there is not enough focus on the latter to cover all the cases. One of the ways attackers find points of interest to further check for vulnerabilities is by identifying the parts of the application that poorly handle malformed inputs. Therefore, you have to rigorously test your application and fix any issues. A popular method of automatically sending malformed inputs to identify flaws in the application is called Fuzzing. In this article, we will understand what fuzzing tools are, how they work, and their purpose. Next, we will learn the differences in open-source fuzzing tools. Finally, we’ll conclude the article with the advantages and disadvantages of fuzzing tools.
Fuzzing, also known as fuzz testing is a method of software testing in which a tool sends malformed data to the application to find implementation bugs. Fuzzing is an iterative process based on an initial template/payload. This is what makes fuzzing different and more relevant with each iteration than just throwing payloads at the wall. However, there are some fuzzing techniques that send random inputs. A fuzzing tool (fuzzer) is a program that automates the process of sending malformed data to the application in an attempt to cause errors. These errors indicate that there might be a bug in the code.
During the development phase, there might not have been enough focus on handling malformed inputs. Even if the developers implemented safe handling of data, it’s hard to tell that they would have thought about all the cases. This is where fuzzing comes in.
The purpose of fuzzing is to identify bugs in the application by analyzing how the application responds to malformed data. Fuzzing adds another point of view to classical software testing techniques (code review, debugging) because of its non-human approach. You should not consider fuzzing as a replacement for other testing techniques but as an addition to these techniques because different methods follow different approaches to finding bugs.
Based on how fuzzers generate inputs, fuzzing can be categorized into 3 major types:
In this type of fuzzing, inputs are randomly generated with no bounds. Depending on the data, sometimes, the application might not even accept the input, or the input might not even be valid. For example, if you fuzz a JSON object to the point where it is not a JSON object, it will not work
In this type of fuzzing, the fuzzer sends an input, understands how the application responds, and then generates subsequent inputs based on the response. Here the fuzzer learns more and more about the application based on the behavior of the application and builds the context. Hence, making it more targeted than random fuzzers.
In this type of fuzzing, the fuzzer generates inputs based on a manually generated template. Individuals who have an idea about the application generate templates so the inputs are not random. The fuzzer uses this template as a reference to generate inputs.
Fuzzing is not just used to simulate user inputs, it can also be used to test programmable interfaces, such as REST APIs and network components.
Now, let’s try to understand how you can improve security with the help of fuzzing tools.
Unlike vulnerability scanners that look for known security weaknesses, fuzzers can help you find weaknesses that are unknown.
Adding this to other testing techniques increases the outcome of security testing. You can find several commercial and open-source fuzzers on the internet, each with its own pros and cons. To help you understand which open-source fuzzing tool is best for you, let us go through the differences in open-source fuzzing tools.
Software fuzzing tools focus on fuzzing various types of software, including desktop and mobile and web applications. Software fuzzing tools can find a wide range of bugs such as crashes, memory leaks, input validation errors, buffer overflows, and more.
Fuzzing is not typically applicable to cloud environments except for specific scenarios such as bucket and instance discovery. The below tools help you setup software fuzzers in cloud environments.
API fuzzing is used to test the security and robustness of application programming interfaces (APIs). It can find bugs such as input validation errors, unexpected responses, and authentication weaknesses
This type of fuzzing involves sending a large number of HTTP requests to a web application with various URL paths and parameters. It can help identify bugs such as misconfigured web servers, and unauthorized access to restricted pages and path traversal issues
This type of fuzzing involves testing the robustness of various network protocols, including TCP/IP, DNS, and SSL/TLS. It can be used to find bugs and vulnerabilities in communication protocols, including network traffic analysis and identification of vulnerabilities in network devices and services.
This type of fuzzing involves testing the robustness of file parsers and other software components that deal with file formats. It can be used to find vulnerabilities such as buffer overflows and other issues related to the parsing and handling of files.
There are not a lot of open-source file format fuzzing tools. Tools like Peach Fuzzer and AFL also provide file format fuzzing. Apart from that, here are some other tools:
The breadth of testing that can be done using fuzzing is impressive. With the wide range of target platforms and tools, fuzzing can really enhance testing.
Fuzzing is a robust method for testing application security with relatively little overhead. Depending on your use case, you can use various types of fuzzing listed above to conduct security testing across your application. In this article, we covered what fuzzing tools are, their purpose, and the different categories of fuzzing.
Fuzzing has become increasingly popular in recent years due to its ability to detect a wide range of bugs and vulnerabilities that traditional testing methods may miss. Fuzzing tools use various techniques to generate inputs that can perform tests in a comprehensive and efficient manner. By incorporating fuzzing into testing strategies, you can enhance the outcome of your testing process. There are various purpose-built tools that are only good at doing exactly what they do. However, it is important to note that it is always recommended to use these tools along with other security testing practices and not as a replacement.
301 Moodie Dr. Unit 108
Ottawa ON K2H 9C4