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Coverage-guided fuzzing for Ruby C extensions uses libFuzzer instrumentation to intelligently explore code paths and detect memory corruption. It targets security-critical code paths in native extensions by feeding malformed inputs to uncover crashes and undefined behavior.

Yes, AddressSanitizer (ASan) and UndefinedBehaviorSanitizer (UBSan) are integrated to detect memory leaks, buffer overflows, and undefined behavior during Ruby gem fuzzing. The sanitizers run alongside libFuzzer to identify critical security vulnerabilities in both pure Ruby code and C extensions.

Running libFuzzer fuzzing campaigns on Ruby applications requires a Clang compiler toolchain and specific sanitizer environment configurations. You must set the appropriate LD_PRELOAD environment variable and execute the ruby command with your target harness script to start the fuzzer.

Coverage-guided fuzzing is needed when you must stress-test Ruby native extensions that handle complex binary data. It ensures extensions remain stable and secure against malformed inputs that could otherwise lead to critical errors like heap-use-after-free vulnerabilities.

The best way to find undefined behavior and crashes in Ruby C extensions is coverage-guided fuzzing with libFuzzer. It intelligently explores code paths to significantly increase the likelihood of finding edge-case bugs that trigger memory corruption and security vulnerabilities.