Fuzzing
Fuzzing, also known as fuzz testing, is a software testing technique where a program is bombarded with intentionally invalid, malformed, or unexpected inputs to identify potential vulnerabilities and bugs in the code by observing how the system reacts to these abnormal inputs, often causing crashes or unexpected behavior that reveal security flaws or coding errors within the application; essentially, it's like "stress testing" a system with random data to see where it breaks down.
Key points about fuzzing:
- How it works: A fuzzer tool generates a large volume of random or semi-random data. It feeds this data to the target application and monitors it for crashes, unexpected behavior, or error messages that indicate a potential vulnerability.
Types of fuzzing:
- Black-box fuzzing: No knowledge of the application's internal workings is required; simply send random inputs and observe the outcome.
- White-box fuzzing: Utilizes knowledge of the source code to generate more targeted inputs that can reach specific parts of the code and potentially trigger more complex vulnerabilities.
- Grey-box fuzzing: A combination of black-box and white-box techniques, leveraging some internal knowledge to improve the effectiveness of fuzzing.
- Mutation-based fuzzing: Starts with a valid input and gradually modifies it by adding, deleting, or changing data bits to create variations and test edge cases.
- Coverage-guided fuzzing: Prioritizes generating inputs that explore new areas of the code by tracking which parts of the code are executed during fuzzing.
What fuzzing can find:
- Buffer overflows: When a program tries to write more data to a memory buffer than it can hold, potentially overwriting adjacent data.
- Denial-of-service (DoS) vulnerabilities: Exploiting flaws in input handling to crash the application or consume excessive resources.
- Cross-site scripting (XSS) vulnerabilities: Injecting malicious JavaScript code into a web application
- SQL injection vulnerabilities: Manipulating database queries with user input to gain unauthorized access to data
Limitations of fuzzing:
- Not exhaustive: Fuzzing cannot guarantee the detection of all vulnerabilities, especially those that don't manifest as crashes or obvious errors.
- Can be time-consuming: Fuzzing can require significant time to generate a large volume of test cases and monitor for potential issues.
- Not suitable for complex logic: Fuzzing might not effectively identify vulnerabilities related to intricate business logic that doesn't directly involve input validation.
Example of fuzzing:
- Testing a file upload feature: A fuzzer would generate various types of files with different sizes, strange file extensions, and corrupted data to see if the application handles them correctly and doesn't crash when attempting to process them.
This is covered in CompTIA CySA+, Pentest+, and Security+.