Understanding CVSS vs EPSS: Which Score Matters More?

The Two Scoring Systems You Need to Know

Every vulnerability gets a CVSS score. Fewer people know about EPSS. If you're only looking at one, you're making decisions with half the picture.

CVSS: The Severity Score

The Common Vulnerability Scoring System (CVSS) rates vulnerabilities on a 0–10 scale based on technical characteristics: attack vector, complexity, privileges required, user interaction, and impact on confidentiality, integrity, and availability.

A CVSS 9.8 means the vulnerability is remotely exploitable, requires no authentication, has low complexity, and can fully compromise the system. Sounds terrifying, and it can be.

But here's the problem: nearly half of all CVEs score 7.0 or higher. That's tens of thousands of "critical" or "high" vulnerabilities every year. No team can patch them all. So which ones do you actually prioritize?

EPSS: The Probability Score

The Exploit Prediction Scoring System (EPSS) takes a fundamentally different approach. Instead of asking "how bad could this be?", it asks "how likely is this to be exploited in the next 30 days?"

EPSS uses machine learning trained on real-world data, CVE metadata, reference tags, exploit code availability, and observed exploitation activity, to produce a probability between 0 and 1.

A vulnerability with CVSS 9.8 but EPSS 0.02 is theoretically devastating but almost never exploited in practice. A vulnerability with CVSS 6.5 but EPSS 0.85 is "medium" severity but is actively being weaponized right now.

Why You Need Both

The magic is in the combination. CVSS tells you the blast radius. EPSS tells you the likelihood of detonation.

The KEV Multiplier

There's a third signal worth watching: CISA's Known Exploited Vulnerabilities (KEV) catalog. If a CVE lands on the KEV list, it's not a prediction anymore, it's confirmed exploitation in the wild. We treat KEV entries as an automatic priority override regardless of CVSS or EPSS scores.

How We Use This

Our platform combines all three signals into a unified risk score tailored to your specific infrastructure. A CVSS 9.8 in a technology you don't use scores zero. A CVSS 6.5 with high EPSS in your exact version of Node.js scores high. Context is everything.

Takeaway

Stop sorting your CVE backlog by CVSS alone. Start combining severity (CVSS), likelihood (EPSS), and confirmed exploitation (KEV) to make decisions that reflect actual risk, not theoretical worst-case scenarios.