A Guide to Using CVSS for Risk Scoring
The Common Vulnerability Scoring System (CVSS) is a widely used framework for assessing the severity of security vulnerabilities. It provides a standardized method for evaluating risks based on key factors such as exploitability, impact, and complexity. Organizations use CVSS scores to prioritize vulnerability remediation and align security efforts with business risk management.
Introduction
The Common Vulnerability Scoring System (CVSS) is a widely used framework for assessing the severity of security vulnerabilities. It provides a standardized method for evaluating risks based on key factors such as exploitability, impact, and complexity. Organizations use CVSS scores to prioritize vulnerability remediation and align security efforts with business risk management.
This guide explains how to use CVSS for risk scoring, including an overview of its components, scoring methodology, and best practices for integrating it into an organization's security strategy.
Understanding CVSS
CVSS is maintained by the Forum of Incident Response and Security Teams (FIRST) and consists of three metric groups:
Base Score Metrics – Represents the fundamental characteristics of a vulnerability.
Temporal Score Metrics – Adjusts the base score based on evolving exploitability.
Environmental Score Metrics – Customizes the score based on the specific environment in which the vulnerability exists.
CVSS Metric Groups Explained
1. Base Score Metrics
The base score measures the intrinsic severity of a vulnerability using the following factors:
Metric | Description |
|---|---|
Attack Vector (AV) | How the vulnerability can be exploited (network, adjacent, local, physical). |
Attack Complexity (AC) | The difficulty of exploiting the vulnerability (low or high). |
Privileges Required (PR) | The level of access needed to exploit the vulnerability (none, low, high). |
User Interaction (UI) | Whether user involvement is required (none or required). |
Scope (S) | Whether the vulnerability affects other system components (changed or unchanged). |
Confidentiality Impact (C) | Potential impact on sensitive information (none, low, high). |
Integrity Impact (I) | The effect on data integrity (none, low, high). |
Availability Impact (A) | The effect on system availability (none, low, high). |
The base score is calculated on a scale from 0 to 10, where:
0.0 – 3.9: Low severity
4.0 – 6.9: Medium severity
7.0 – 8.9: High severity
9.0 – 10.0: Critical severity
2. Temporal Score Metrics
Temporal metrics adjust the base score based on:
Exploit Code Maturity (E) – How easy it is to exploit the vulnerability (unproven, proof-of-concept, functional, or high).
Remediation Level (RL) – The availability of fixes (official fix, temporary fix, workaround, or unavailable).
Report Confidence (RC) – The reliability of the vulnerability report (unknown, reasonable, confirmed).
3. Environmental Score Metrics
Environmental metrics allow organizations to adjust CVSS scores based on business impact:
Confidentiality, Integrity, and Availability Requirements (CR, IR, AR) – How important these factors are to the organization (low, medium, high).
Modified Base Metrics – Organizations can modify any base metric based on their unique environment.
How to Use CVSS for Risk Scoring
Step 1: Identify and Assess Vulnerabilities
Use automated security tools (e.g., vulnerability scanners, SAST/DAST tools) to detect vulnerabilities and retrieve their CVSS scores from databases like:
NVD (National Vulnerability Database)
MITRE CVE List
Vendor Security Advisories
Step 2: Calculate the CVSS Score
Use the CVSS calculator provided by FIRST (https://www.first.org/cvss/calculator/3.1) to determine the base, temporal, and environmental scores.
Step 3: Prioritize Vulnerabilities Based on Risk Impact
After calculating the CVSS score, use a risk-based approach to prioritize vulnerabilities:
Critical (9.0 – 10.0): Immediate remediation required.
High (7.0 – 8.9): Remediate as soon as possible.
Medium (4.0 – 6.9): Fix in regular patch cycles.
Low (0.1 – 3.9): Address when resources allow.
Step 4: Implement a Risk-Based Remediation Strategy
Patch Management: Apply fixes based on CVSS severity.
Compensating Controls: If a patch isn’t available, apply mitigations such as firewall rules or access restrictions.
Exception Handling: Document and assess risks if vulnerabilities cannot be patched immediately.
Step 5: Monitor and Update Scores Regularly
Vulnerabilities evolve over time, requiring continuous monitoring. Use threat intelligence feeds to reassess CVSS scores and adjust priorities accordingly.
Best Practices for Using CVSS
Don’t Rely Solely on CVSS Base Scores – Use environmental factors to adjust risk assessment based on business impact.
Automate CVSS Score Calculation – Integrate CVSS scoring with security tools and vulnerability management platforms.
Incorporate Business Context – Not all high-CVSS vulnerabilities pose the same level of risk to every organization.
Use CVSS Scores to Support Decision-Making – Align vulnerability remediation with security policies and risk management strategies.
Regularly Train Security Teams – Ensure security professionals understand how to interpret and apply CVSS scores effectively.
Conclusion
CVSS provides a standardized way to assess and prioritize vulnerabilities based on severity and business impact. By leveraging CVSS scores in vulnerability management workflows, organizations can:
Improve security risk assessment.
Prioritize remediation effectively.
Enhance compliance and governance.
By integrating CVSS into a risk-based security strategy, organizations can allocate resources efficiently and maintain a proactive security posture.