A fuzzer is automated test software that sends a program large numbers of unusual, malformed, or randomly varied inputs to trigger crashes, hangs, memory errors, and other hidden bugs. Instead of checking one expected case at a time, fuzzing explores how software behaves under stress and edge conditions.
In cyber security, fuzzers are one of the most effective ways to find vulnerabilities before attackers do. They are widely used against browsers, file parsers, media libraries, and network services because these components process untrusted data at scale. Security teams use fuzzing to catch issues such as buffer overflows, use-after-free bugs, and parser logic flaws. Attackers can also fuzz targets to map weak spots and turn crashes into reliable exploits. Good defenses rely on continuous fuzzing, crash triage, and patching, especially for complex code like web browsers where a single input path can expose a large attack surface.