MITRE Corporation

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. It 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.

Availability

There is 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 has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to 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 a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

High

Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

There is no impact to availability within the impacted component.

None

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Such conditions may require the collection of more information about the target or computational exceptions. The assessment of this metric excludes any requirements for user interaction in order to exploit the vulnerability. 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.

Attack Complexity

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. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.

These metrics enable the analyst to customize the CVSS score depending on the importance of the Availability of the affected IT asset to a user’s organization, relative to other impacts. This metric modifies the environmental score by reweighting the Modified Availability impact metric versus the other modified impacts.

Availability Requirement

Loss of Availability is likely to have a catastrophic adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

Loss of Availability is likely to have only a limited adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

Assigning this value to the metric will not influence the score.

Medium

Assigning this value indicates there is insufficient information to choose one of the other values, and has no impact on the overall Environmental Score, i.e., it has the same effect on scoring as assigning Medium.

Not Defined

This metric reflects the context by which vulnerability exploitation is possible. The Base Score increases the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable component.

Attack Vector

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).

Adjacent

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., tricking a legitimate user into opening a malicious document).

Local

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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).

Network

The attack requires the attacker to physically touch or manipulate the vulnerable component. Physical interaction may be brief or persistent.

Physical

This metric measures the impact to 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.

Confidentiality

There is 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.

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.

There is no loss of confidentiality within the impacted component.

These metrics enable the analyst to customize the CVSS score depending on the importance of the Confidentiality of the affected IT asset to a user’s organization, relative to other impacts. This metric modifies the environmental score by reweighting the Modified Confidentiality impact metric versus the other modified impacts.

Confidentiality Requirement

Loss of Confidentiality is likely to have a catastrophic adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

Loss of Confidentiality is likely to have only a limited adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

This metric measures the likelihood of the vulnerability being attacked, and is typically based on the current state of exploit techniques, exploit code availability, or active, 'in-the-wild' exploitation.

Exploit Code Maturity

Functional exploit code is available. The code works in most situations where the vulnerability exists.

Functional

Functional autonomous code exists, or no exploit is required (manual trigger) and details are widely available. Exploit code works in every situation, or is actively being delivered via an autonomous agent (such as a worm or virus). Network-connected systems are likely to encounter scanning or exploitation attempts. Exploit development has reached the level of reliable, widely-available, easy-to-use automated tools.

Proof-of-concept exploit code is available, or an attack demonstration is not practical for most systems. The code or technique is not functional in all situations and may require substantial modification by a skilled attacker.

Proof-of-Concept

No exploit code is available, or an exploit is theoretical.

Unproven

Assigning this value indicates there is insufficient information to choose one of the other values, and has no impact on the overall Temporal Score, i.e., it has the same effect on scoring as assigning High.

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

Integrity

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to 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 to the impacted component.

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.

There is no loss of integrity within the impacted component.

These metrics enable the analyst to customize the CVSS score depending on the importance of the Integrity of the affected IT asset to a user’s organization, relative to other impacts. This metric modifies the environmental score by reweighting the Modified Integrity impact metric versus the other modified impacts.

Integrity Requirement

Loss of Integrity is likely to have a catastrophic adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

Loss of Integrity is likely to have only a limited adverse effect on the organization or individuals associated with the organization (e.g., employees, customers).

Modified Availability

The value assigned to the corresponding Base metric is used.

Modified Attack Complexity

This metric reflects the context by which vulnerability exploitation is possible. The Environmental Score increases the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable component.

Modified Attack Vector

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).

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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.

Modified Confidentiality

Modified Integrity

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

Modified Privileges Required

The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.

The attacker is authorized with (i.e., 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 may have the ability to cause an impact only to non-sensitive resources.

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.

Does a successful attack impact a component other than the vulnerable component? If so, the Base Score increases and the Confidentiality, Integrity and Authentication metrics should be scored relative to the impacted component.

Modified Scope

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.

Changed

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.

Unchanged

This metric captures the requirement for a user, other than the attacker, to participate in the successful compromise 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.

Modified User Interaction

The vulnerable system can be exploited without any interaction from any user.

Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.

Required

Privileges Required

This metric measures the degree of confidence in the existence of the vulnerability and the credibility of the known technical details. Sometimes only the existence of vulnerabilities are publicized, but without specific details. For example, an impact may be recognized as undesirable, but the root cause may not be known. The vulnerability may later be corroborated by research which suggests where the vulnerability may lie, though the research may not be certain. Finally, a vulnerability may be confirmed through acknowledgement by the author or vendor of the affected technology. The urgency of a vulnerability is higher when a vulnerability is known to exist with certainty. This metric also suggests the level of technical knowledge available to would-be attackers.

Report Confidence

Detailed reports exist, or functional reproduction is possible (functional exploits may provide this). Source code is available to independently verify the assertions of the research, or the author or vendor of the affected code has confirmed the presence of the vulnerability.

Confirmed

Significant details are published, but researchers either do not have full confidence in the root cause, or do not have access to source code to fully confirm all of the interactions that may lead to the result. Reasonable confidence exists, however, that the bug is reproducible and at least one impact is able to be verified (Proof-of-concept exploits may provide this). An example is a detailed write-up of research into a vulnerability with an explanation (possibly obfuscated or 'left as an exercise to the reader') that gives assurances on how to reproduce the results.

Reasonable

There are reports of impacts that indicate a vulnerability is present. The reports indicate that the cause of the vulnerability is unknown, or reports may differ on the cause or impacts of the vulnerability. Reporters are uncertain of the true nature of the vulnerability, and there is little confidence in the validity of the reports or whether a static Base score can be applied given the differences described. An example is a bug report which notes that an intermittent but non-reproducible crash occurs, with evidence of memory corruption suggesting that denial of service, or possible more serious impacts, may result.

Unknown

Assigning this value indicates there is insufficient information to choose one of the other values, and has no impact on the overall Temporal Score, i.e., it has the same effect on scoring as assigning Confirmed.

The Remediation Level of a vulnerability is an important factor for prioritization. The typical vulnerability is unpatched when initially published. Workarounds or hotfixes may offer interim remediation until an official patch or upgrade is issued. Each of these respective stages adjusts the temporal score downwards, reflecting the decreasing urgency as remediation becomes final.

Remediation Level

A complete vendor solution is available. Either the vendor has issued an official patch, or an upgrade is available.

Official Fix

There is an official but temporary fix available. This includes instances where the vendor issues a temporary hotfix, tool, or workaround.

Temporary Fix

There is either no solution available or it is impossible to apply.

Unavailable

There is an unofficial, non-vendor solution available. In some cases, users of the affected technology will create a patch of their own or provide steps to work around or otherwise mitigate the vulnerability.

Workaround

Assigning this value indicates there is insufficient information to choose one of the other values, and has no impact on the overall Temporal Score, i.e., it has the same effect on scoring as assigning Unavailable.

Scope

User Interaction

Choosing Message Identifier

Force the System to Reset Values

Using Unpublished Interfaces or Functionality

Cross Site Request Forgery

Communication Channel Manipulation

The product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.

Divide the software into anonymous, normal, privileged, and administrative areas. Identify which of these areas require a proven user identity, and use a centralized authentication capability.

For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…

Where possible, avoid implementing custom, "grow-your-own" authentication routines and consider using authentication capabilities as provided by the surrounding framework, operating system, or environment.

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

Missing Authentication for Critical Function

Authentication

Credential Stuffing

Forgot Password

Session Management

Identification and Authentication Failures

OWASP Authentication Cheat Sheet

Authentication Failures

Use centralized authentication mechanism

Mutually authenticate application components. Minimize privileges

Consistently apply authentication strength

MITRE CWE

MITRE CAPEC

OWASP Top 10

OWASP OpenCRE

Metasploit Framework

ProjectDiscovery nuclei-templates

Exploit-DB

CVE Program CNA list

FIRST CVSS v3.1

FIRST CVSS v4.0

CVE-2025-63391 is a high-severity vulnerability classified under CWE-306 (Missing Authentication for Critical Function). It allows remote attackers to gain unauthorized read access to sensitive data without authentication or user interaction. The affected versions are all versions up to and including 0.6.32. There is no information about available patches or fixes, and no known exploits have been observed in the wild as of the publication date.

CVE Database V5

Detailed information about CVE-2025-63391: n/a. Get real-time updates, technical details, and mitigation strategies.

CVE-2025-63391 has been rejected

Official rejection reason