Why Security Teams Should Use KEV and EPSS Alongside CVSS for Patching

The Common Vulnerability Scoring System (CVSS) measures theoretical severity but cannot indicate whether a vulnerability is being actively exploited, making it insufficient as a sole prioritization tool. CISA's Known Exploited Vulnerabilities (KEV) catalog lists CVEs confirmed as actively exploited in the wild, while FIRST's Exploit Prediction Scoring System (EPSS) uses machine learning to estimate the probability of exploitation within 30 days. Security teams scanning thousands of vulnerabilities can use KEV matches and high EPSS scores to identify the most urgent threats, rather than defaulting to CVSS rankings alone. For example, a CVSS 9.8 flaw with no known exploits may be less urgent than a lower-scored vulnerability already appearing in the KEV catalog. Combining all three signals — KEV, EPSS, and CVSS — gives practitioners a more accurate, risk-based approach to vulnerability remediation.