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Auth.js: Configuration errors can cause existence-based auth checks to fail open (auth object populated with an error)

Critical severity GitHub Reviewed Published Jul 20, 2026 in nextauthjs/next-auth • Updated Aug 12, 2026

Package

npm next-auth (npm)

Affected versions

>= 5.0.0-beta.0, <= 5.0.0-beta.31

Patched versions

5.0.0-beta.32

Description

Impact

next-auth (Auth.js) v5 applications that gate access by checking only for the existence of the auth object — the pattern shown in the official session management / protecting resources guide — are affected.

When the Auth.js configuration produces a server-side error, the auth object exposed by the auth() wrapper (in middleware, Route Handlers, etc.) is populated with an error object instead of being null:

{ "message": "There was a problem with the server configuration. Check the server logs for more information." }

Because this object is truthy, any authorization check of the form !!auth (or if (req.auth)) evaluates to true for every request, including unauthenticated ones. The application fails open: instead of denying access when the auth layer is broken, it grants access to everyone.

// middleware.ts — affected pattern
export default auth((req) => {
  const { nextUrl, auth } = req
  const isLoggedIn = !!auth // <-- always true when the configuration is broken
  // ...
})

A representative trigger is a provider that is missing required configuration. For example, a Keycloak provider with neither issuer nor authorization endpoint set logs:

[auth][error] InvalidEndpoints: Provider "keycloak" is missing both `issuer` and `authorization` endpoint config. At least one of them is required.

…and from that point on auth is the error object above, so !!auth is permanently true. The same fail-open behavior occurs for other server-configuration errors (for example, an unset AUTH_SECRET).

There is no impact while the configuration is valid. The risk materializes when a previously-working deployment becomes misconfigured — e.g. an environment variable is changed or removed during a deploy — at which point existence-based auth checks silently stop protecting routes and all visitors are treated as authenticated. Because the failure mode is silent and grants access to everyone, the consequences can be severe.

This is an instance of CWE-636 (Not Failing Securely / "Failing Open") leading to improper authorization (CWE-285).

Patches

The fix ensures that a server-configuration error no longer surfaces as a truthy auth object: existence checks fail closed rather than open. This is released in next-auth@<!-- TODO: set patched version on publish -->.

To upgrade:

npm i next-auth@beta
yarn add next-auth@beta
pnpm add next-auth@beta

Workarounds

If you cannot upgrade immediately, check for a concrete user/session property rather than the bare object, so a configuration-error object is not treated as an authenticated session:

// middleware.ts
export default auth((req) => {
  // `auth.user` is only present on a real session; resilient to config-error objects
  const isLoggedIn = !!req.auth?.user
  // ...
})

As defense in depth, make Auth.js configuration errors fail loudly in your deployment pipeline (for example, treat [auth][error] log lines as a failed health check) so a broken configuration cannot silently reach production. As always, an existing session indicates authentication only — for authorization, perform an explicit role/permission check rather than relying on session existence. See the role-based access control guide.

References

For more information

If you have any concerns, Auth.js requests responsible disclosure, outlined here: https://authjs.dev/security

Credits

Reported by @marc-zollingkoffer-syzygy.

References

@gustavovalverde gustavovalverde published to nextauthjs/next-auth Jul 20, 2026
Published to the GitHub Advisory Database Jul 23, 2026
Reviewed Jul 23, 2026
Last updated Aug 12, 2026

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. 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 severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. 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.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM 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.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM 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 system, this metric refers to the loss of availability of the impacted system 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 a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM 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.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM 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 system, this metric refers to the loss of availability of the impacted system 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 a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(48th percentile)

Weaknesses

Improper Authorization

The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Learn more on MITRE.

Not Failing Securely ('Failing Open')

When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions. Learn more on MITRE.

CVE ID

CVE-2026-73421

GHSA ID

GHSA-8fpg-xm3f-6cx3

Source code

Credits

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