5 Ways Fuzz Testing Catches Bugs Your Tests Miss

What is fuzz testing? Apart from its really cool name, what is it and how is it supposed to help you catch sneaky bugs?

Fuzz testing is an automated testing technique that involves using inputting random, unexpected, malformed data into your application to try and break it. By automating this process, fuzz testing enables a tester, you, to sniff out bugs that might have been missed when crafting test case scenarios. It’s really awesome!

So let’s consider five ways you could use fuzz testing to catch bugs that your current testing techniques might have missed, consequently improving your system’s reliability.

1. Early Detection of Vulnerabilities

According to IBM's Systems Sciences Institute, fixing bugs in production costs up to 100 times more than that if they had been fixed in development.

This is why we test, to eliminate as many bugs as we can before they get into production. However, tests like unit and integrations simply verifies expected behaviours. Fuzz testing on the other hand caters for unexpected scenarios by testing your application with thousands of unexpected inputs, enabling even more detection of bugs in development.

By integrating fuzz testing into your development workflow, you'll eliminate more bugs in development, which would result in fewer production incidents and significant reduced maintenance costs.

2. Comprehensive Coverage

Having 100% test coverage doesn't guarantee quality software.

Your tests covering every code in your project don’t necessarily mean your test cases extensively cover numerous test cases, which is what fuzz testing gets you. When you integrate fuzz testing into your software testing processes, you’ll be able to cover a wide variety of test cases and user inputs, which include malformed data and unexpected input combinations.

You can use tools like American Fuzzy Lop (AFL) to generate these test cases, helping you confirm not just that your code is tested (code coverage) but that they’re tested extensively. This way your test coverage isn’t just confirming that your code is tested but that they’re extensively tested.

By including fuzz testing in your software testing pipeline, you will increase your confidence in your test coverage and application’s reliability.

3. Memory & Concurrency Bugs

Memory and concurrency bugs are some of the hardest issues to debug because they often appear randomly and are hard to reproduce. They often don't become apparent until they're in production, where they become more expensive to resolve.

Fuzz testing has proven to be an effective way of debugging memory and concurrency issues by generating various inputs that trigger memory and thread-related issues. It can identify buffer overflows by sending oversized inputs, catch use-after-free errors by manipulating memory allocation timing, and expose race conditions by testing different thread interactions. Tools like libFuzzer are particularly effective at detecting these types of bugs as they offer memory sanitization features in addition to regular fuzzing features.

By implementing fuzz testing in your software testing processes, you'll be able to identify and fix tricky memory and concurrency bugs before they get into production.

4. Improved Reliability & Stability

You can’t possibly predict every single way users will interact with your application. It is impossible. This doesn’t stop users from losing confidence in your application though when they experience a crash as a result of an unexpected use case.

Fuzz testing seeks to improve reliability and stability by testing your application against a wide range of unexpected inputs. By continuously generating and testing different unexpected or malformed inputs, fuzz testing enables you to identify potential crash testing that you’d have missed with manual or traditional testing strategies that use expected test cases. You can even take it on step further by Integrating fuzz testing into your CI/CD pipeline.

Integrating fuzz testing into your CI/CD pipeline ensures that every code change is automatically tested against these scenarios, maintaining your application's reliability throughout development, and helping you reduce crashes in production and overall user experience.

5. Detect Vulnerabilities with External Libraries

External libraries make building software faster, but they can also be a source of vulnerabilities, even well-maintained ones.

Fuzz testing extends beyond just testing your application code. It’s just as effective on testing external libraries as it is on your own code. By generating various malformed inputs and unexpected usage patterns, fuzz testing can uncover memory and race condition issues in external libraries. Tools like LibFuzzer are great for this, helping you expose potential vulnerabilities that could compromise your entire application.

By fuzz-testing external libraries, you'll ensure that every component of your system, whether built in-house or external, maintains the same level of reliability and security.

You Should Give It A Try

If you have little experience with fuzz testing, you can start by picking up a beginner-friendly tool like AFL and trying it on your project. It’s open source and has great support and documentation. There are also other tools like LibFuzzer and Go Fuzz, if you’re working with Go.

References

• What Is Fuzz Testing, And How Does It Work?

• Detecting Kernel Memory Bugs through Inconsistent Memory Management Intention Inferences

• Cost of Fixing Defects