CVE-2026-45109: Next Next.js Has A Middleware / Vulnerability

HIGH
Advisory Identifier: GHSA-26hh-7cqf-hhc6
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CVSS 7.5
CWE-288
Published
Advisory Summary

CVE-2026-45109 is a HIGH (CVSS 7.5) next.js has a middleware / vulnerability (CWE-288: Authentication Bypass Using an Alternate Path or Channel) affecting Next libraries in the npm ecosystem. The issue involves next.js has a middleware / proxy bypass in app router applications via segment-prefetch routes - incomplete fix follow-up. Remediation is available by upgrading affected packages to version 15.5.18, 16.2.6.

CVE-2026-45109 at a Glance

CVE Identifier CVE-2026-45109
GHSA Identifier GHSA-26hh-7cqf-hhc6
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-288: Authentication Bypass Using an Alternate Path or Channel
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-2026-45109

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: 15.5.18 
npm install next@15.5.18
next fixed: 16.2.6 
npm install next@16.2.6
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-2026-45109, 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 15.5.18), 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-288: Authentication Bypass Using an Alternate Path or Channel, where the product requires authentication, but the product has an alternate path or channel that does not require authentication. 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 It was found that the fix addressing [CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f) did not apply to `middleware.ts` with Turbopack. Refer to [CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f) for further details. ### References - [CVE CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f)

CVE-2026-45109 Affected Next Versions

2 component(s)
Fixed Versions:
15.5.1816.2.6
Product / Package Ecosystem Affected Versions Fixed Version
next
npm/next
npm
≥ 15.2.0
< 15.5.18
15.5.18
next
npm/next
npm
≥ 16.0.0
< 16.2.6
16.2.6

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f
GitHub Advisory / Wiki ADVISORY
https://github.com/vercel/next.js/security/advisories/GHSA-26hh-7cqf-hhc6
NVD — CVE-2026-45109 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45109
Next Source Repository REPOSITORY
https://github.com/vercel/next.js
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v15.5.18
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v16.2.6

Frequently Asked Questions

What is CVE-2026-45109?
CVE-2026-45109 is a security vulnerability in Next involving Next.js has a Middleware / Proxy bypass in App Router applications via segment-prefetch routes - Incomplete Fix Follow-Up under CWE-288: Authentication Bypass Using an Alternate Path or Channel.
Which Next versions are affected?
Affected versions include releases prior to 15.5.18, 16.2.6 across affected packages: next.
What version fixes CVE-2026-45109?
Upgrading to 15.5.18, 16.2.6 (or the latest patched release for your respective branch) resolves the vulnerability.
Is next affected?
Yes, next is affected in releases prior to 15.5.18, 16.2.6. Upgrade your dependency to 15.5.18, 16.2.6 or later.
What is the CVSS score of CVE-2026-45109?
CVE-2026-45109 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-2026-45109?
CVE-2026-45109 is classified under CWE-288: Authentication Bypass Using an Alternate Path or Channel (The product requires authentication, but the product has an alternate path or channel that does not require authentication.).
How can I check npm dependencies for CVE-2026-45109?
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-26hh-7cqf-hhc6",
  "modified" : "2026-05-14T20:39:01Z",
  "published" : "2026-05-11T16:21:19Z",
  "aliases" : [ "CVE-2026-45109" ],
  "summary" : "Next.js has a Middleware / Proxy bypass in App Router applications via segment-prefetch routes - Incomplete Fix Follow-Up",
  "details" : "### Impact\n\n\nIt was found that the fix addressing [CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f) did not apply to `middleware.ts` with Turbopack. Refer to  [CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f) for further details.\n\n### References \n\n- [CVE CVE-2026-44575](https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f)",
  "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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      "ecosystem" : "npm",
      "name" : "next"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
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      }, {
        "fixed" : "15.5.18"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
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    "ranges" : [ {
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  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/security/advisories/GHSA-267c-6grr-h53f"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/security/advisories/GHSA-26hh-7cqf-hhc6"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45109"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/vercel/next.js"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/releases/tag/v15.5.18"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/vercel/next.js/releases/tag/v16.2.6"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-288" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-11T16:21:19Z",
    "nvd_published_at" : "2026-05-13T18:16:19Z"
  }
}