CVSS
The Common Vulnerability Scoring System (CVSS) is an open framework for communicating the characteristics and severity of software vulnerabilities. CVSS consists of three metric groups: Base, Temporal, and Environmental. The Base group represents the intrinsic qualities of a vulnerability that are constant over time and across user environments, the Temporal group reflects the characteristics of a vulnerability that change over time, and the Environmental group represents the characteristics of a vulnerability that are unique to a user’s environment.
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. This document provides the official specification for CVSS version 3.1.
Attack Vector (AV)
This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the Base Score) will be larger the more remote (logically, and physically) an attacker can be to exploit the vulnerable component. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater Base Score.
- Network (N): The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers). An example of a network attack is an attacker causing a denial of service (DoS) by sending a specially crafted TCP packet across a wide area network (e.g., CVE‑2004‑0230).
- Adjacent (A): The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE‑2013‑6014).
- Local (L): The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either:
- The attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or
- The attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
- Physical (P): The attack requires the attacker to physically touch or manipulate the vulnerable component. Physical interaction may be brief (e.g., evil maid attack[^1]) or persistent. An example of such an attack is a cold boot attack, in which an attacker gains access to disk encryption keys after physically accessing the target system. Other examples include peripheral attacks via FireWire/USB Direct Memory Access (DMA).
cvss -> av: Attack Vector (AV) score.
- n: Network (N)
- a: Adjacent (A)
- l: Local (L)
- p: Physical (P)Attack Complexity (AC)
This metric describes the conditions beyond the attacker’s control that must exist to exploit the vulnerability. As described below, such conditions may require the collection of more information about the target, or computational exceptions. Importantly, the assessment of this metric excludes any requirements for user interaction to exploit the vulnerability (such conditions are captured in the User Interaction metric). If a specific configuration is required for an attack to succeed, the Base metrics should be scored assuming the vulnerable component is in that configuration. The Base Score is greatest for the least complex attacks.
- Low (L): Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
- High (H): A successful attack depends on conditions beyond the attacker’s control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected.[^2] For example, a successful attack may depend on an attacker overcoming any of the following conditions:
- The attacker must gather knowledge about the environment in which the vulnerable target/component exists. For example, a requirement to collect details on target configuration settings, sequence numbers, or shared secrets.
- The attacker must prepare the target environment to improve exploit reliability. For example, repeated exploitation to win a race condition, or overcoming advanced exploit mitigation techniques.
- The attacker must inject themselves into the logical network path between the target and the resource requested by the victim to read and/or modify network communications (e.g., a man in the middle attack).
cvss -> ac: Attack Complexity (AC) score.
- l: Low (L)
- h: High (H)Privileges Required (PR)
This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. The Base Score is greatest if no privileges are required.
- None (N): The attacker is unauthorized before the attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
- Low (L): The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges can access only non-sensitive resources.
- High (H): The attacker requires privileges that provide significant (e.g., administrative) control over the vulnerable component, allowing access to component-wide settings and files.
cvss -> pr: Privileges Required (PR) score.
- n: None (N)
- l: Low (L)
- h: High (H)User Interaction (UI)
This metric captures the requirement for a human user, besides the attacker, to participate in the successful compromise of the vulnerable component. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner. The Base Score is greatest when no user interaction is required.
- None (N): The vulnerable system can be exploited without interaction from any user.
- Required (R): Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited. For example, a successful exploit may only be possible during the installation of an application by a system administrator.
cvss -> ui: User Interaction (UI) score.
- n: None (N)
- r: Required (R)Scope (S)
The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.
- Unchanged (U): An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
- Changed (C): An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
cvss -> s: Scope (S) score.
- u: Unchanged (U)
- c: Changed (C)Confidentiality (C)
This metric measures the impact on the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones. The Base Score is greatest when the loss to the impacted component is highest.
- High (H): There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator’s password, or private encryption keys of a web server.
- Low (L): There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
- None (N): There is no loss of confidentiality within the impacted component.
cvss -> c: Confidentiality (C) score.
- h: High (H)
- l: Low (L)
- n: None (N)Integrity (I)
This metric measures the impact on integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. The Base Score is greatest when the consequence on the impacted component is highest.
- High (H): There is a total loss of integrity, or a complete loss of protection. For example, the attacker can modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence on the impacted component.
- Low (L): Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
- None (N): There is no loss of integrity within the impacted component.
cvss -> i: Integrity (I) score.
- h: High (H)
- l: Low (L)
- n: None (N)Availability (A)
This metric measures the impact on the availability of the impacted component resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the impacted component, this metric refers to the loss of availability of the impacted component itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of an impacted component. The Base Score is greatest when the consequence on the impacted component is highest.
- High (H): There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker can deny some availability, but the loss of availability presents a direct, serious consequence on the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks an only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
- Low (L): Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker can’t completely deny service to legitimate users. The resources in the impacted component are either partially available all the time, or fully available only some time, but overall, there is no direct, serious consequence on the impacted component.
- None (N): There is no impact to availability within the impacted component.
cvss -> a: Availability (A) score.
- h: High (H)
- l: Low (L)
- n: None (N)Global Score
All the Base metrics produce a score ranging from 0.0 (less dangerous) to 10.0 (more dangerous).
cvss -> score: Global score (1.0 "-" to 10.0 "+").Severity
The Global Score generates a Severity:
n– None: 0.0l– Low: 0.1 to 3.9m– Medium: 4.0 to 6.9h– High: 7.0 to 8.9c– Critical: 9.0 to 10.0
Exploitability
Level of exploitability, ranging from 0.0 (less exploitable) to 10.0 (more exploitable).
cvss -> exploitable: Exploitability (1.0 "-" to 10.0 "+").Global impact
Level of global impact, ranging from 0.0 (less impact) to 10.0 (more impact).
cvss -> impact: Global impact (1.0 "-" to 10.0 "+").CWE
CWE (Common Weakness Enumeration) is a community-developed list of software and hardware weakness types. It serves as a common language, a measuring stick for security tools, and as a baseline for weakness identification, mitigation, and prevention efforts. There are around 1,000 identifications.
data -> vulnerability -> impact -> cwe
data -> vulnerability -> impact -> cwe -> cwe: CWE identificator.
data -> vulnerability -> impact -> cwe -> name: Name.
data -> vulnerability -> impact -> cwe -> description: Description.