EPSS vs. CVSS: Which is Better for Vulnerability Prioritization?

Introduction

Vulnerability management is a critical aspect of cybersecurity, ensuring that organizations address security weaknesses before they can be exploited. Traditionally, the Common Vulnerability Scoring System (CVSS) has been the go-to method for assessing the severity of vulnerabilities. However, as cyber threats become more dynamic, the Exploit Prediction Scoring System (EPSS) has emerged as an alternative approach. But which one is better for vulnerability prioritization? Let’s dive in.

What is CVSS?

CVSS (Common Vulnerability Scoring System) is an open framework used to assess the severity of security vulnerabilities. It assigns a score between 0 and 10, where higher scores indicate more severe vulnerabilities.

CVSS Scoring Components:

1. Base Score: Measures the intrinsic properties of a vulnerability (e.g., attack vector, impact on confidentiality, integrity, and availability).
2. Temporal Score: Adjusts the base score based on factors like exploitability and remediation availability.
3. Environmental Score: Further refines the score based on specific security configurations within an organization.

Strengths of CVSS:

? Industry-standard, widely accepted framework. ? Provides a structured way to evaluate vulnerabilities. ? Offers consistency in vulnerability assessment.

Limitations of CVSS:

? CVSS does not consider real-world exploitation likelihood. ? Many high-scoring vulnerabilities are never exploited in the wild. ? Prioritization based on CVSS alone may lead to wasted remediation efforts.

What is EPSS?

EPSS (Exploit Prediction Scoring System) is a machine learning-based model developed by FIRST.org to estimate the likelihood that a vulnerability will be exploited in the wild within the next 30 days. Instead of static severity ratings, EPSS provides a probability score (0 to 1) based on real-world threat intelligence and attack trends.

How EPSS Works:

• Uses historical attack data, exploit reports, and CVE characteristics.
• Continuously updates based on new cyber threat intelligence.
• Prioritizes vulnerabilities that pose immediate, real-world risks.

Strengths of EPSS:

? Data-driven approach focused on exploitability. ? Helps prioritize vulnerabilities that attackers are actively exploiting. ? Reduces alert fatigue by filtering out low-risk vulnerabilities.

Limitations of EPSS:

? Does not measure the impact of exploitation, only probability. ? Might miss high-impact vulnerabilities that haven’t been exploited yet. ? Requires integration with other risk assessment frameworks.

EPSS vs. CVSS: Head-to-Head Comparison

FeatureCVSSEPSSScoring Range0 - 100 - 1 (0% to 100%)FocusSeverity of vulnerabilityLikelihood of exploitationData SourceStatic attributes of the vulnerabilityReal-world exploitation data, ML modelsUpdate FrequencyInfrequent (when CVE is published)Dynamic, based on live threat intelligenceBest ForGeneral risk assessmentActive threat-based prioritization

Which One is Better for Vulnerability Prioritization?

The best approach depends on the use case:

• Use CVSS when you need a standardized measure of vulnerability severity, especially for compliance and reporting.
• Use EPSS when you need to prioritize threats based on real-world attack likelihood and reduce remediation workload.
• Best Practice: Combine both for a risk-based vulnerability management approach—filter high-impact vulnerabilities using CVSS, then prioritize based on EPSS scores.

Conclusion

Neither CVSS nor EPSS alone is a perfect solution for vulnerability management. While CVSS provides severity assessment, EPSS helps predict real-world risks. The most effective strategy is a hybrid approach, leveraging CVSS for impact evaluation and EPSS for exploitation likelihood, ensuring organizations focus their efforts on the most pressing security threats.