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CVE-2026-53721 – Authentication Bypass – Nuxt.js 3.11.0–3.21.6 and 4.0.0–4.4.6

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Summary

CVE-2026-53721 is a high-severity authentication bypass vulnerability in Nuxt.js, the open-source Vue.js web development framework. Affecting versions 3.11.0 through 3.21.6 and 4.0.0 through 4.4.6, the flaw allows unauthenticated, network-based attackers to bypass route-rule middleware protections entirely by exploiting a case-sensitivity mismatch between vue-router and the routeRules matcher. It carries a CVSS v4.0 score of 8.8 (HIGH).

Technical details

  • Root cause: Vue-router resolves routes using case-insensitive path matching (its default sensitive: false setting), while Nuxt’s compiled routeRules matcher — built on the rou3 library — performs case-sensitive comparisons. The two components therefore disagree on whether a given URL matches a protected route.
  • Trigger conditions: An application is vulnerable when it uses routeRules.appMiddleware to enforce access controls (e.g., authentication gates, authorization checks). No special configuration or elevated privileges are required; any deployment relying on routeRules for access control within the affected version range is at risk.
  • Attack vector: A remote, unauthenticated attacker submits an HTTP request with altered casing in a static segment of a protected URL — for example, requesting /Admin/dashboard instead of /admin/dashboard. The vue-router matches and renders the route, but the routeRules lookup (getRouteRules({ path: to.path })) fails to find a corresponding rule, causing the middleware to be skipped entirely.
  • Impact: The server returns a fully server-side-rendered page without executing the intended middleware, potentially exposing protected content, sensitive SSR-captured data, or restricted functionality. Affected route rules include appMiddleware, ssr, redirect, appLayout, and prerender/payload hints. Authorization logic defined via definePageMeta({ middleware }) on individual components is not affected by this bypass.

Affected software

  • Nuxt.js 3.11.0 through 3.21.6 (inclusive)
  • Nuxt.js 4.0.0 through 4.4.6 (inclusive)

Severity

  • CVSS v4.0 score: 8.8 (HIGH)
  • CVSS v4.0 vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N
  • CWE-178: Improper Handling of Case Sensitivity
  • CWE-863: Incorrect Authorization

Mitigation and recommended actions

  • Immediate – upgrade to a patched version:
    • Nuxt 3.x users: upgrade to 3.21.7 or later
    • Nuxt 4.x users: upgrade to 4.4.7 or later
  • Interim workarounds (if patching is not immediately possible):
    • Enable case-sensitive routing globally by setting router.options.sensitive = true in your Nuxt configuration, aligning vue-router’s behavior with the routeRules matcher.
    • Relocate all authorization logic from routeRules.appMiddleware to definePageMeta({ middleware }) on each protected page component, which is not affected by this bypass.
    • Enforce authorization at the API and data-fetching layer as a defence-in-depth measure, independent of route-level middleware.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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