Understanding CVSS Severity Levels and Ratings | Complete Guide for 2025

Table of Contents

• What is CVSS?
• Purpose of CVSS
• CVSS Score Metrics: The Three Metric Groups
• CVSS Score Ranges and Severity Ratings
• CVSS Version History
• How to Calculate a CVSS Score
• Why CVSS Scoring Matters
• CVSS in Action: Example
• Limitations of CVSS
• CVSS and CVE: What’s the Difference?
• Best Practices for Using CVSS in Organizations
• CVSS vs. Other Scoring Systems
•  Conclusion
• Frequently Asked Questions (FAQs)

Understanding the Common Vulnerability Scoring System (CVSS) is crucial for cybersecurity professionals, developers, and IT managers to assess the severity of security vulnerabilities. In this blog, we’ll explore the CVSS ratings, how they are calculated, and why they matter in vulnerability management.

What is CVSS?

The Common Vulnerability Scoring System (CVSS) is a standardized framework for rating the severity of security vulnerabilities in software systems. It provides a numerical score ranging from 0.0 to 10.0, which corresponds to a qualitative rating (e.g., Low, Medium, High, Critical). This helps organizations prioritize their responses based on risk.

CVSS is maintained by FIRST (Forum of Incident Response and Security Teams) and is widely used in CVEs (Common Vulnerabilities and Exposures) and vulnerability databases.

Purpose of CVSS

• Quantify the severity of security vulnerabilities.

• Allow consistent risk assessment across organizations.

• Aid in patch prioritization and vulnerability management.

• Facilitate communication between vendors, researchers, and users.

CVSS Score Metrics: The Three Metric Groups

CVSS scoring is composed of three metric groups:

1. Base Metrics (Mandatory)

These reflect the intrinsic characteristics of a vulnerability.

• Attack Vector (AV) – How the vulnerability is exploited (network, adjacent, local, physical).

• Attack Complexity (AC) – Conditions beyond the attacker's control.

• Privileges Required (PR) – Level of privileges an attacker needs.

• User Interaction (UI) – Whether user interaction is required.

• Scope (S) – Whether the exploited vulnerability affects resources beyond its security scope.

• Confidentiality (C) – Impact on information confidentiality.

• Integrity (I) – Impact on data integrity.

• Availability (A) – Impact on system availability.

2. Temporal Metrics (Optional)

These reflect the current status of the vulnerability:

• Exploit Code Maturity – Is the exploit publicly available?

• Remediation Level – Is there a fix or workaround?

• Report Confidence – How confident is the information?

3. Environmental Metrics (Optional)

Customized based on an organization’s security posture and environment:

• Security Requirements (CR, IR, AR) – Confidentiality, Integrity, Availability requirements.

• Modified Base Metrics – Adjusted metrics for local context.

 CVSS Score Ranges and Severity Ratings

These categories are often used in vulnerability management dashboards to prioritize patching efforts.

 CVSS Version History

 How to Calculate a CVSS Score

You can calculate CVSS scores using:

• The official CVSS calculator provided by FIRST.

• Integrated tools in vulnerability scanners like Nessus, OpenVAS, Qualys, or Rapid7.

• API integrations with vulnerability management platforms.

For example, a vulnerability with:

• Network attack vector,

• Low attack complexity,

• No privileges required,

• No user interaction,

• High impact on confidentiality, integrity, and availability
  … might score 9.8 – Critical.

 Why CVSS Scoring Matters

1. Helps prioritize patching: Fix critical vulnerabilities first.

2. Supports compliance: Required by standards like PCI-DSS, ISO 27001.

3. Improves reporting: Clear communication of risk to stakeholders.

4. Risk-based decision-making: Balances urgency with business impact.

 CVSS in Action: Example

Imagine a vulnerability in a widely used library that allows remote code execution (RCE) without user interaction. The CVSS score might look like this:

• AV: Network

• AC: Low

• PR: None

• UI: None

• C: High

• I: High

• A: High

This would typically result in a score of 9.8 (Critical).

Limitations of CVSS

• It doesn’t account for exploitability in your specific environment.

• It may over-prioritize certain issues while underestimating others.

• Doesn’t reflect the business impact directly.

That’s why it’s recommended to combine CVSS with threat intelligence, asset value, and business context for effective risk assessment.

CVSS and CVE: What’s the Difference?

• CVSS is the scoring system.

• CVE (Common Vulnerabilities and Exposures) is the unique ID for each known vulnerability.

• CVE records often include CVSS scores to reflect the severity.

Best Practices for Using CVSS in Organizations

• Automate CVSS-based scoring in your vulnerability scanners.

• Don’t rely solely on CVSS for prioritization.

• Use environmental metrics to reflect your actual risk.

• Train your team to interpret CVSS effectively.

 CVSS vs. Other Scoring Systems

 Conclusion

The CVSS framework is a powerful tool for measuring and communicating the severity of vulnerabilities. While not perfect, it offers a standardized, industry-recognized method to help organizations assess and prioritize their cybersecurity risks.

Understanding how to interpret and use CVSS scores—alongside threat context and asset value—is a key skill in modern vulnerability management.

FAQs

What is CVSS in cybersecurity?

CVSS stands for Common Vulnerability Scoring System, a framework used to assess the severity of security vulnerabilities based on a numerical score and qualitative ratings.

How is a CVSS score calculated?

A CVSS score is calculated using base, temporal, and environmental metrics such as attack vector, complexity, privileges required, and impact on confidentiality, integrity, and availability.

What are the severity levels in CVSS?

CVSS severity levels include None (0.0), Low (0.1–3.9), Medium (4.0–6.9), High (7.0–8.9), and Critical (9.0–10.0).

What is considered a high CVSS score?

A score between 7.0 and 8.9 is considered "High," and anything above 9.0 is "Critical," indicating severe risk.

What is a good CVSS score?

A "good" score is subjective, but generally, a lower score (below 4.0) indicates lower risk and is more manageable.

What is CVSS v4.0?

CVSS version 4.0 is the latest update released in 2023, introducing new metrics for IoT/ICS systems and refining scoring accuracy.

Who uses CVSS scores?

Security analysts, system administrators, vulnerability management teams, and organizations use CVSS scores to prioritize vulnerability fixes.

What’s the difference between CVSS and CVE?

CVE is a unique identifier for a vulnerability, while CVSS is a scoring system used to rate its severity.

Can CVSS scores change over time?

Yes, scores may be updated as more information becomes available or as environments change, particularly with temporal and environmental metrics.

How accurate is the CVSS system?

CVSS is widely accepted but not perfect; it should be used alongside other risk assessment tools for better accuracy.

What are base metrics in CVSS?

Base metrics include attack vector, complexity, required privileges, user interaction, and the impact on confidentiality, integrity, and availability.

What are temporal metrics in CVSS?

These metrics account for the current state of exploit code, remediation availability, and report confidence.

What are environmental metrics in CVSS?

These adjust the base score to better reflect an organization’s specific risk posture and asset value.

Where can I find CVSS scores for vulnerabilities?

CVSS scores are published in vulnerability databases such as NVD (National Vulnerability Database) and MITRE’s CVE list.

Why are CVSS scores important?

They help prioritize which vulnerabilities need to be patched first based on severity and risk level.

How do I use CVSS in my organization?

Integrate it into your vulnerability scanners and use the scores to inform patching policies and risk assessments.

Are there tools to calculate CVSS scores?

Yes, the official CVSS calculator by FIRST and integrations in tools like Nessus, Qualys, and OpenVAS provide scoring features.

What is a CVSS score of 10?

A score of 10.0 represents the highest level of risk and typically indicates a remotely exploitable, critical vulnerability.

How often is CVSS updated?

CVSS is periodically updated by FIRST; the latest version is 4.0, released in 2023.

Is CVSS scoring mandatory?

While not legally mandatory, it is considered an industry best practice for cybersecurity risk assessment.

What is CVSS safety metric in v4.0?

The new Safety (S) metric in CVSS v4.0 considers the physical harm a vulnerability might cause, especially for IoT and embedded systems.

How do businesses use CVSS scores?

Businesses use CVSS to inform patch cycles, compliance requirements, and threat prioritization.

What does a CVSS score of 5.0 mean?

A 5.0 score falls under "Medium" severity, indicating a moderate level of risk.

Can a CVSS score be wrong?

Yes, especially if calculated using incomplete or outdated information. That’s why manual verification is often necessary.

What is CVSS exploitability score?

This is a component of the overall score that reflects how easy it is to exploit a given vulnerability.

What is the difference between CVSS base and environmental score?

Base score is standard and unchanging, while environmental score is adjusted to reflect organizational risk.

Can I trust automated CVSS scores?

Automated scores are a good starting point but should be validated within the context of your environment.

What is the purpose of CVSS?

Its purpose is to standardize the assessment of vulnerability severity, making communication and prioritization easier.

Is CVSS open-source?

Yes, CVSS is an open standard maintained by FIRST and publicly available for use and integration.

What is FIRST in CVSS?

FIRST (Forum of Incident Response and Security Teams) is the organization that develops and maintains the CVSS framework.