Fuzz testing has become the de facto standard for vulnerability discovery. In this paper we study 32 prominent protocol implementations that have been continuously fuzzed by OSS-Fuzz, a widely used fuzzing platform. We define metrics to measure fuzzing activity within a project and correlate our measurements with registered CVEs for discovered vulnerabilities. Our analysis show a strong correlation between fuzzing activity and registered CVEs within a project. However, by using the CWE-1000 analys framework, we find that the correlation is only strong for certain classes of vulnerabilities.