Vulnerability Metrics

The Common Vulnerability Scoring System (CVSS) is a method used to supply a qualitative measure of severity. CVSS is not a measure of risk. CVSS consists of three metric groups: Base, Temporal, and Environmental. The Base metrics produce a score ranging from 0 to 10, which can then be modified by scoring the Temporal and Environmental metrics. A CVSS score is also represented as a vector string, a compressed textual representation of the values used to derive the score. Thus, CVSS is well suited as a standard measurement system for industries, organizations, and governments that need accurate and consistent vulnerability severity scores. Two common uses of CVSS are calculating the severity of vulnerabilities discovered on one's systems and as a factor in prioritization of vulnerability remediation activities. The National Vulnerability Database (NVD) provides CVSS scores for almost all known vulnerabilities.

The NVD supports both Common Vulnerability Scoring System (CVSS) v2.0 and v3.X standards. The NVD provides CVSS 'base scores' which represent the innate characteristics of each vulnerability. The NVD does not currently provide 'temporal scores' (metrics that change over time due to events external to the vulnerability) or 'environmental scores' (scores customized to reflect the impact of the vulnerability on your organization). However, the NVD does supply a CVSS calculator for both CVSS v2 and v3 to allow you to add temporal and environmental score data.

CVSS is owned and managed by FIRST.Org, Inc. (FIRST), a US-based non-profit organization, whose mission is to help computer security incident response teams across the world. The official CVSS documentation can be found at  https://www.first.org/cvss/.

NVD CVSS Calculators

NVD CVSS v2 Calculator		NVD CVSS v3 Calculator

NVD Vulnerability Severity Ratings

NVD provides qualitative severity ratings of "Low", "Medium", and "High" for CVSS v2.0 base score ranges in addition to the severity ratings for CVSS v3.0 as they are defined in the CVSS v3.0 specification.

CVSS v2.0 Ratings		CVSS v3.0 Ratings
Severity	Base Score Range	Severity	Base Score Range
		None	0.0
Low	0.0-3.9	Low	0.1-3.9
Medium	4.0-6.9	Medium	4.0-6.9
High	7.0-10.0	High	7.0-8.9
		Critical	9.0-10.0

NVD Specific CVSS Information

Incomplete Data

With some vulnerabilities, all of the information needed to create CVSS scores may not be available. This typically happens when a vendor announces a vulnerability but declines to provide certain details. In such situations, NVD analysts assign CVSS scores using a worst case approach. Thus, if a vendor provides no details about a vulnerability, NVD will score that vulnerability as a 10.0 (the highest rating).

Collaboration with Industry

NVD staff are willing to work with the security community on CVSS impact scoring. If you wish to contribute additional information or corrections regarding the NVD CVSS impact scores, please send email to nvd@nist.gov. We actively work with users that provide us feedback.

Legacy CVSS Information

As of July 13th, 2022, the NVD no longer generates Vector Strings, Qualitative Severity Ratings, or Severity Scores for CVSS v2. Existing CVSS v2 information will remain in the database but the NVD will no longer actively populate CVSS v2 for new CVEs. This change comes as CISA policies that rely on NVD data fully transition away from CVSS v2. NVD analysts will continue to use the reference information provided with the CVE and any publicly available information at the time of analysis to associate Reference Tags, CVSS v3.1, CWE, and CPE Applicability statements.

The NVD began supporting the CVSS v3.1 guidance on September 10th, 2019. The NVD will not be offering CVSS v3.0 and v3.1 vector strings for the same CVE. All new and re-analyzed CVEs will be done using the CVSS v3.1 guidance.

Vector strings for the CVE vulnerabilities published between to 11/10/2005 and 11/30/2006 have been upgraded from CVSS version 1 data. CVSS v1 metrics did not contain granularity of CVSS v2 and so these scores are marked as "Version 2.0 upgrade from v1.0" within NVD. While these scores are approximation, they are expected to be reasonably accurate CVSSv2 scores.

Vector strings provided for the 13,000 CVE vulnerabilities published prior to 11/9/2005 are approximated from only partially available CVSS metric data. In particular, the following CVSS metrics are only partially available for these vulnerabilities and NVD assumes certain values based on an approximation algorithm: Access Complexity, Authentication, Confidentiality Impact of 'partial', Integrity Impact of 'partial', Availability Impact of 'partial', and the impact biases.