CVE-2026-64643: Next Unauthenticated Disclosure Of Internal Server Vulnerability

MODERATE
Advisory Identifier: GHSA-955p-x3mx-jcvp
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CWE-201
Published
Advisory Summary

CVE-2026-64643 is a MODERATE unauthenticated disclosure of internal server vulnerability (CWE-201: Insertion of Sensitive Information Into Sent Data) affecting Next libraries in the npm ecosystem. The issue involves unauthenticated disclosure of internal server function endpoints. Remediation is available by upgrading affected packages to version 15.5.21, 16.2.11.

CVE-2026-64643 at a Glance

CVE Identifier CVE-2026-64643
GHSA Identifier GHSA-955p-x3mx-jcvp
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-201: Insertion of Sensitive Information Into Sent Data
Affected Product Next
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-64643

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: 15.5.21 
npm install next@15.5.21
next fixed: 16.2.11 
npm install next@16.2.11
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-2026-64643, 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 15.5.21), 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-201: Insertion of Sensitive Information Into Sent Data, where the code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor. 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 In Next.js applications using App Router, Server Actions (`use server`) or `use cache` endpoints can be disclosed bypassing any authentication on the pages where these endpoints are usually used. Server Action IDs can be disclosed to unauthenticated users via publicly served client artifacts (for example, static chunks containing action references). Affected users are applications using App Router + Server Actions. By itself, this disclosure is typically a recon/enumeration primitive; however, it can increase risk when combined with other weaknesses. ## Workarounds Never assume any authentication claims at the `use cache` or `use server` boundary. Always authenticate within the boundary.

CVE-2026-64643 Affected Next Versions

2 component(s)
Fixed Versions:
15.5.2116.2.11
Product / Package Ecosystem Affected Versions Fixed Version
next
npm/next
npm
≥ 13.0.0
< 15.5.21
15.5.21
next
npm/next
npm
≥ 16.0.0
< 16.2.11
16.2.11

References

GitHub Advisory / Wiki ADVISORY
https://github.com/vercel/next.js/security/advisories/GHSA-955p-x3mx-jcvp
Security Fix Commit FIX COMMIT
https://github.com/vercel/next.js/commit/1b0c3ae912a3ad925c60065cc8d55b070fa8bcd3
Security Fix Commit FIX COMMIT
https://github.com/vercel/next.js/commit/ff12a6124e1504f17b62de948b8a553fdecaef7b
Next Source Repository REPOSITORY
https://github.com/vercel/next.js
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v15.5.21
Next Release RELEASE
https://github.com/vercel/next.js/releases/tag/v16.2.11

Frequently Asked Questions

What is CVE-2026-64643?
CVE-2026-64643 is a security vulnerability in Next involving Unauthenticated disclosure of internal Server Function endpoints under CWE-201: Insertion of Sensitive Information Into Sent Data.
Which Next versions are affected?
Affected versions include releases prior to 15.5.21, 16.2.11 across affected packages: next.
What version fixes CVE-2026-64643?
Upgrading to 15.5.21, 16.2.11 (or the latest patched release for your respective branch) resolves the vulnerability.
Is next affected?
Yes, next is affected in releases prior to 15.5.21, 16.2.11. Upgrade your dependency to 15.5.21, 16.2.11 or later.
What CWE is associated with CVE-2026-64643?
CVE-2026-64643 is classified under CWE-201: Insertion of Sensitive Information Into Sent Data (The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.).
How can I check npm dependencies for CVE-2026-64643?
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 
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  "schema_version" : "1.4.0",
  "id" : "GHSA-955p-x3mx-jcvp",
  "modified" : "2026-07-22T23:00:34Z",
  "published" : "2026-07-22T23:00:34Z",
  "aliases" : [ "CVE-2026-64643" ],
  "summary" : "Next.js: Unauthenticated disclosure of internal Server Function endpoints",
  "details" : "## Impact\n\nIn Next.js applications using App Router, Server Actions (`use server`) or `use cache` endpoints can be disclosed bypassing any authentication on the pages where these endpoints are usually used.\n\nServer Action IDs can be disclosed to unauthenticated users via publicly served client artifacts (for example, static chunks containing action references).\n\nAffected users are applications using App Router + Server Actions.  \n\nBy itself, this disclosure is typically a recon/enumeration primitive; however, it can increase risk when combined with other weaknesses.\n \n## Workarounds\n\nNever assume any authentication claims at the `use cache` or `use server` boundary. Always authenticate within the boundary.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N"
  } ],
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}