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Application security testingIntermediate

Fuzz Testing

Fuzz testing sends generated, mutated, malformed, or unexpected inputs to software to reveal crashes, hangs, memory errors, state problems, and unsafe behavior.

What it means

Fuzzers may be coverage-guided, grammar-aware, mutation-based, or protocol-specific. Effective campaigns require useful seed inputs, instrumentation, triage, and reproducible test cases.

Why it matters

Fuzzing explores input combinations that humans may not anticipate and can uncover serious reliability and security defects before adversaries do.

Practical focus

  • Choose targets with meaningful input surfaces
  • Preserve crashing inputs and execution context
  • Minimize and reproduce failures
  • Add fixed cases to regression testing

Common mistakes

  • Running a fuzzer without monitoring crashes
  • Fuzzing only a friendly test harness
  • Counting executions instead of useful coverage
  • Closing crashes without root-cause analysis

Certification relevance

This subject appears in or supports the following certification bodies of knowledge:

ISC2 CSSLPCompTIA PenTest+

Authoritative sources