Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-73421 – Authentication Bypass – NextAuth.js (next-auth) 5.0.0-beta.4 through 5.0.0-beta.31

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-73421 is an improper authorization vulnerability in NextAuth.js (Auth.js) v5 that causes the library to fail open rather than fail closed when the server encounters a configuration error. Applications that authorize requests by simply checking for the existence of the auth object (e.g., if (req.auth) or !!auth) can be tricked into granting access to unauthenticated users once a misconfiguration occurs. The issue carries a CVSS score of 9.1 (Critical).

Technical details

  • Root cause: when Auth.js hits a server configuration error (e.g., a missing AUTH_SECRET, or a provider missing both the issuer and authorization endpoint, triggering InvalidEndpoints), it parses the resulting non-OK session response into a truthy error object instead of returning null.
  • Trigger condition: the bypass only manifests after a deployment becomes misconfigured; in a correctly configured environment there is no impact.
  • Attack vector: Network — no authentication or user interaction is required to exploit a misconfigured instance; the flaw is reachable through any protected route, middleware, Route Handler, or React Server Component that gates access via auth().
  • Impact: routes and pages protected solely by "does an auth object exist" logic silently grant access to unauthenticated visitors, resulting in an authorization bypass with high confidentiality and integrity impact.

Affected software

  • next-auth (NextAuth.js / Auth.js v5) versions 5.0.0-beta.0 through 5.0.0-beta.31

Severity

  • CVSS Score: 9.1 (Critical)
  • CVSS v4.0 Vector: 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

Mitigation and recommended actions

  • Immediate: Upgrade to next-auth version 5.0.0-beta.32 or later, which fixes the fail-open behavior.
  • If immediate patching isn’t possible:
    • Change authorization checks to validate a concrete session property rather than mere object existence, e.g. const isLoggedIn = !!req.auth?.user instead of !!req.auth.
    • Treat Auth.js error log lines as failed health checks at the deployment level so misconfigured builds are prevented from reaching production.
    • Rely on role-based access control decisions rather than solely on session presence for authorization.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge