How severe is CVE-2026-53721?

No CVSS score has been assigned to CVE-2026-53721 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-53721?

CVE-2026-53721 affects the following packages: nuxt (npm), nuxt (npm). Ecosystems affected: npm.

How do I fix CVE-2026-53721?

Update nuxt to 4.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53721 is resolved across your whole dependency graph.

How do I detect CVE-2026-53721 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nuxt, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-53721 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-53721 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-53721 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-53721?

CVE-2026-53721 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 34th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-53721?

CVE-2026-53721 is classified as CWE-178 (CWE-178), CWE-863 (CWE-863). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-53721 published, and has it been updated?

CVE-2026-53721 was published on June 12, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2026-53721 — nuxt

Fix: nuxt/nuxt@07e39cd

CVE-2026-53721 is a CWE-178 vulnerability in nuxt. A fix is available for nuxt — see the affected versions and patch details below.

Nuxt: Route-rule middleware bypass via case-sensitivity mismatch between vue-router and the routeRules matcher

Also known asGHSA-mm7m-92g8-7m47

Published

Jun 12, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53721.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

777other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

nuxtnpm

3.3Mdownloads / week

Description

Impact

Nuxt looks up routeRules for the current navigation by calling getRouteRules({ path: to.path }) from the page-router plugin and the no-pages router plugin. The compiled routeRules matcher (built on rou3) performs case-sensitive matching, while vue-router is configured with its default sensitive: false and matches paths case-insensitively.

The two routers therefore disagree on which rules apply to a given request path: vue-router still matches the page record for /Admin/dashboard, but the routeRules lookup for the same path returns no match. Any appMiddleware declared via routeRules is never added to the middleware set and never runs, on both SSR and client navigations. The same path skips other path-keyed route rules in the same way (ssr, redirect, appLayout, and the prerender / payload hints used client-side).

For applications using routeRules with appMiddleware as an authorization gate (a documented pattern), an attacker can flip the case of any static segment in a protected URL (for example /Admin/dashboard instead of /admin/dashboard) to render the protected page with the middleware skipped. The server returns the fully server-rendered page including any useFetch / useAsyncData results captured during SSR.

This is an instance of CWE-178 (Improper Handling of Case Sensitivity) leading to CWE-863 (Incorrect Authorization) for apps that treat appMiddleware as an authorization boundary.

Mitigating factors

Only affects apps that use routeRules.appMiddleware. The more idiomatic definePageMeta({ middleware }) is bound to the matched route record and is unaffected.
Nuxt route middleware is documented as an app-layer concern, not a server-side auth boundary; well-built apps enforce authorization again at the API / data-fetching layer.
Apps that explicitly set router.options.sensitive = true are not affected.

Patches

Fixed in [email protected] (commit 07e39cd6) and backported to [email protected] (commit 3f3e3fa7). The fix normalizes the path used for routeRules lookups so it matches vue-router's default case-insensitive semantics.

Workarounds

Until you can upgrade, you can mitigate by either:

Setting router.options.sensitive = true so vue-router matches case-sensitively (this changes route-matching behaviour app-wide).
Moving security-critical middleware off routeRules.appMiddleware and onto definePageMeta({ middleware: [...] }) on the protected page components, which is bound to the matched record.
Enforcing authorization at the API / data-fetching layer (which you should be doing in any case).

Credit

Reported by Anthropic / Claude through Anthropic's coordinated vulnerability disclosure process. Reference: ANT-2026-9FSEBYMC.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`nuxt`	≥ 4.0.0&&< 4.4.7	4.4.7`npm install nuxt@4.4.7`
📦npm	`nuxt`	≥ 3.11.0&&< 3.21.7	3.21.7`npm install nuxt@3.21.7`

Affected Products

1 product · 2 configurations

Application

nuxtnuxt

≥ 4.0.0 && < 4.4.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for nuxt, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update nuxt to 4.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53721 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

## Impact Nuxt looks up `routeRules` for the current navigation by calling `getRouteRules({ path: to.path })` from the page-router plugin and the no-pages router plugin. The compiled `routeRules` matcher (built on `rou3`) performs case-sensitive matching, while vue-router is configured with its default `sensitive: false` and matches paths case-insensitively. The two routers therefore disagree on which rules apply to a given request path: vue-router still matches the page record for `/Admin/dashboard`, but the `routeRules` lookup for the same path returns no match. Any `appMiddleware` declare

O3 Security · Impact-Aware SCA

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