structural:expansion
Vulnerabilities

Imagine a website has 100 text input boxes. A few are vulnerable to SQL injections on certain strings. Submitting random strings to those boxes for a while will hopefully hit the bugged code path. The error shows itself as a broken HTML page half rendered because of an SQL error. In this case, only text boxes are treated as input streams. However, software systems have many possible input streams, such as cookie and session data, the uploaded file stream, RPC channels, or memory. Errors can happen in any of these input streams. The test goal is to first get an unhandled error and then understand the flaw based on the failed test case. Testers write an automated tool to test their understanding of the flaw until it is correct. After that, it may become obvious how to package the payload so that the target system triggers its execution. If this is not viable, one can hope that another error produced by the fuzzer yields more fruit. The use of a fuzzer saves time by not checking adequate code paths where exploits are unlikely.