CVSS Frequently Asked Questions

What is CVSS?

A: CVSS stands for The Common Vulnerability Scoring System and is a vendor agnostic, industry open standard designed to convey vulnerability severity and help determine urgency and priority of response. It solves the problem of multiple, incompatible scoring systems and is usable and understandable by anyone.

Who developed CVSS?

A: CVSS was commissioned by the National Infrastructure Advisory Council (NIAC) tasked in support of the global Vulnerability Disclosure Framework. It is currently maintained by FIRST (Forum of Incident Response and Security Teams). CVSS was a joint effort involving many groups including:

Since the original release of CVSS, additional groups have joined the CVSS effort and assisted in developing version 2 of CVSS. The current list of major participants is available at http://www.first.org/cvss/team.

What does CVSS not do?

A: CVSS is not a threat scoring system (DHS color warning system), a vulnerability database or a veal-time attack scoring system.

What is involved in CVSS?

A: The CVSS model is designed to provide the end user with an overall composite score representing the severity and risk of a vulnerability. It is derived from metrics and formulas. The metrics are in three distinct categories that can be quantitatively or qualitatively measured. Base Metrics contain qualities that are intrinsic to any given vulnerability that do not change over time or in different environments.Temporal Metrics contain characteristics of a vulnerability which evolve over the lifetime of vulnerability. Environmental Metrics contain those characteristics of a vulnerability which are tied to an implementation in a specific users environment.

What is the current version of CVSS?

A: The current version of CVSS is version 2. It was finalized and released to the public in June 2007. This FAQ addresses CVSS version 2 only, although there are many similarities between versions 1 and 2. Information on CVSS version 1 is available from the NIAC Paper on CVSS at http://www.first.org/cvss/cvss-dhs-12-02-04.pdf

What are the details of the Base Metrics?

A: There are six Base Metrics which represent the most fundamental, immutable qualities of a vulnerability.

a) Access Vector measures how remote an attacker can be to attack a target.

b) Access Complexity measures the complexity of attack required to exploit the vulnerability once an attacker has gained access to the target system.

c) Authentication measures the number of times an attacker must authenticate to the target system in order to exploit the vulnerability.

d) Confidentiality Impact measures the impact on confidentiality of a successful exploit of the vulnerability on the target system.

e) Integrity Impact measures the impact on integrity of a successful exploit of the vulnerability on the target system.

f) Availability Impact measures the impact on availability of a successful exploit of the vulnerability on the target system.

What are the details of the Temporal Metrics?

A: There are three Temporal Metrics which represent the time dependent qualities of a vulnerability.

a) Exploitability measures how complex the process is to exploit the vulnerability in the target system.

b) Remediation Level measures the level of an available solution.

c) Report Confidence measures the degree of confidence in the existence of the vulnerability and the credibility of its report.

What are the details of the Environment Metrics?

A: There are three Environmental Metrics which represent the implementation and environment specific qualities of a vulnerability.

a) Collateral Damage Potential measures the potential for a loss of life or physical assets through damage or theft of property or equipment.

b) Target Distribution measures the relative size of the field of target systems susceptible to the vulnerability.

c) Impact Requirement allows a score to be customized depending on the criticality of the affected IT asset, such as giving greater weight to availability if an asset supports a business function for which availability is most important. The impact requirement is a set of three metrics: confidentiality, integrity, and availability. The possible values for each metric are:

How is the scoring done?

A: Scoring is the process of combining all the metric values according to specific formulas.

Base Scoring is computed by the vendor or originator with the intention of being published and once set, is not expected to change. It is computed from the big three confidentiality, integrity and availability. This is the foundation which is modified by the Temporal and Environmental metrics. The base score has the largest bearing on the final score and represents vulnerability severity.

Temporal Scoring is also computed by vendors and coordinators for publication, and modifies the Base score. It allows for the introduction of mitigating factors to reduce the score of a vulnerability and is designed to be re-evaluated at specific intervals as a vulnerability ages. The temporal score represents vulnerability urgency at specific points in time.

Environmental Scoring is optionally computed by end-user organizations and adjusts combined Base-Temporal score. This should be considered the FINAL score and represents a snapshot in time, tailored to a specific environment. User organizations should use this to prioritize responses within their own environments

Is there an easier way to understand all this?

A: Yes. This flowchart shows each metric group and how they interrelate with each other.

Where can I get the hardcore details of the scoring formulas?

A: Full details on the CVSS version 2 formulas are available from A Complete Guide to the Common Vulnerability Scoring System Version 2.0, at www.first.org/cvss/cvss-guide.html.

Who is using CVSS?

A: NIAC was submitted to the President in January 2005. DHS (Department of Homeland Security) and CVSS developers are encouraging widespread, voluntary adoption. Many organizations have since adopted CVSS, including several NIAC member companies (Akamai, American Water, Symantec, Union Pacific) and other organizations (CERT/CC, Cisco, HP, IBM, NIST, Oracle, Qualys, US-CERT).

I am an end-user (CISO/CSO/operations security person), is there anything I need to do?

A: Typically, application and security product vendors will provide both the Baseand Temporal scores. As the end user, you need only calculate your Environmental score.

I am an application or product security vendor, why should I use CVSS and publish CVSS temporal scores?

A: As more vendors begin publishing CVSS scores, more customers will understand and appreciate the advantages. They will grow to appreciate the ability to tailor scores to their environment and begin expect CVSS scores of all their suppliers. The more it is used, the better it works.

I am an end-user, and really like other vendors scoring methods, why should I change to CVSS?

A: Other systems are closed competing standards, do not offer a mutable scoring framework, and do not consider different environments.

What does CVSS really offer that other scoring methodologies do not?

A: An open framework that can be used, understood, and improved upon by anybody to score vulnerabilities.

Where can I get CVSS scores?

A: There are many sources of CVSS scores. Several major sources of CVSS scores are posted at http://www.first.org/cvss/scores.html.

Where can I get the CVSS code?

A: CVSS is a framework that you can use to develop an application suitable to your needs, your environment or your customers. There is no established code as of yet. However, there are several CVSS calculators available; a listing of some calculators is posted at www.first.org/cvss/scores.html.

How can I help establish CVSS through out the industry?

A: Urge your vendors to support CVSS scoring.

Where can I get more information on CVSS?

A: You can get more information at FIRST, the current custodian for CVSS at http://www.first.org/cvss/. Documentation on CVSS metrics, formulas, and scoring is available a http://www.first.org/cvss/cvss-guide.html.