CVE-2026-44573: Next Next.js Has A Middleware / Vulnerability

HIGH
Advisory Identifier: GHSA-36qx-fr4f-26g5
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CVSS 7.5
CWE-863
Published
Advisory Summary

CVE-2026-44573 is a HIGH (CVSS 7.5) next.js has a middleware / vulnerability (CWE-863: Incorrect Authorization) affecting Next libraries in the npm ecosystem. The issue involves next.js has a middleware / proxy bypass in pages router applications using i18n. Remediation is available by upgrading affected packages to version 15.5.16, 16.2.5.

CVE-2026-44573 at a Glance

CVE Identifier CVE-2026-44573
GHSA Identifier GHSA-36qx-fr4f-26g5
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-863: Incorrect Authorization
Affected Product Next
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-44573

To remediate this vulnerability, upgrade all affected Next dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

next fixed: 15.5.16 
npm install next@15.5.16
next fixed: 16.2.5 
npm install next@16.2.5
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls next

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-44573, inspect your project dependencies using npm:

npm ls next

Analyze the terminal output to locate any version of Next in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 15.5.16), your application is affected.

Note: The npm ls next command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-863: Incorrect Authorization, where the product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. In Next, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Applications using the Pages Router with `i18n` configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less `/_next/data/<buildId>/<page>.json` requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks. ### Fix The matcher logic was updated to perform the same match as it would on a non-i18n data route. ### Workarounds If you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.

CVE-2026-44573 Affected Next Versions

2 component(s)
Fixed Versions:
15.5.1616.2.5
Product / Package Ecosystem Affected Versions Fixed Version
next
npm/next
npm
≥ 12.2.0
< 15.5.16
15.5.16
next
npm/next
npm
≥ 16.0.0
< 16.2.5
16.2.5

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vercel/next.js/security/advisories/GHSA-36qx-fr4f-26g5
NVD — CVE-2026-44573 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-44573
Next Source Repository REPOSITORY
https://github.com/vercel/next.js
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v15.5.16
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v16.2.5

Frequently Asked Questions

What is CVE-2026-44573?
CVE-2026-44573 is a security vulnerability in Next involving Next.js has a Middleware / Proxy bypass in Pages Router applications using i18n under CWE-863: Incorrect Authorization.
Which Next versions are affected?
Affected versions include releases prior to 15.5.16, 16.2.5 across affected packages: next.
What version fixes CVE-2026-44573?
Upgrading to 15.5.16, 16.2.5 (or the latest patched release for your respective branch) resolves the vulnerability.
Is next affected?
Yes, next is affected in releases prior to 15.5.16, 16.2.5. Upgrade your dependency to 15.5.16, 16.2.5 or later.
What is the CVSS score of CVE-2026-44573?
CVE-2026-44573 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2026-44573?
CVE-2026-44573 is classified under CWE-863: Incorrect Authorization (The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.).
How can I check npm dependencies for CVE-2026-44573?
Run the dependency tree command: 'npm ls next'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-36qx-fr4f-26g5",
  "modified" : "2026-05-14T20:37:59Z",
  "published" : "2026-05-11T15:53:51Z",
  "aliases" : [ "CVE-2026-44573" ],
  "summary" : "Next.js has a Middleware / Proxy bypass in Pages Router applications using i18n",
  "details" : "### Impact\n\nApplications using the Pages Router with `i18n` configured and middleware/proxy-based authorization can allow unauthorized access to protected page data through locale-less `/_next/data/<buildId>/<page>.json` requests. In affected configurations, middleware does not run for the unprefixed data route, allowing an attacker to retrieve SSR JSON for protected pages without passing the intended authorization checks.\n\n### Fix\nThe matcher logic was updated to perform the same match as it would on a non-i18n data route.\n\n### Workarounds\n\nIf you cannot upgrade immediately, enforce authorization in the page's server-side data path instead of relying solely on middleware.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
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      "name" : "next"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
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      }, {
        "fixed" : "15.5.16"
      } ]
    } ]
  }, {
    "package" : {
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      "name" : "next"
    },
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      } ]
    } ]
  } ],
  "references" : [ {
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    "type" : "ADVISORY",
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  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/vercel/next.js"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/releases/tag/v15.5.16"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/releases/tag/v16.2.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-863" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T15:53:51Z",
    "nvd_published_at" : "2026-05-13T17:16:22Z"
  }
}