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CVE-2026-64643 — next

Fix: vercel/next.js@1b0c3ae

CVE-2026-64643 is a CWE-201 vulnerability in next. A fix is available for next — see the affected versions and patch details below.

Next.js: Unauthenticated Disclosure of Internal Server Function endpoints

Also known asGHSA-955p-x3mx-jcvp
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Oct 22, 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.
  • 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-2026-64643.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk
0.01%0.35%0.68%1.02%0.5%0.5%0.5%0.5%Aug 26Oct 26Oct 26

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.

61Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
nextnpm
41.1Mdownloads / week

Description

Next.js is a React framework for building full-stack web applications. In versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, 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 and Server Actions. By itself, this disclosure is typically a recon/enumeration primitive; however, it can increase risk when combined with other weaknesses. This issue has been fixed in versions 15.5.21 and 16.2.11.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
📦npmnext≥ 13.0.0&&< 15.5.2115.5.21npm install next@15.5.21
📦npmnext≥ 16.0.0&&< 16.2.1116.2.11npm install next@16.2.11

Affected Products

1 product · 2 configurations
Application
next.jsvercel
≥ 16.0.0 && < 16.2.11
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update next to 15.5.21 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-64643 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This Moderate information disclosure vulnerability in Next.js applications allows unauthenticated users to obtain Server Action IDs from publicly served client artifacts. While primarily a reconnaissance primitive, this exposure could increase overall risk when chained with other weaknesses. Red Hat products and…

Workaround published by Red Hat
Upstream advises that applications should never assume authentication claims at the `use server` (Server Action) or `use cache` boundary: always perform authentication checks within the Server Action or cached function itself rather than relying on page-level authentication or on Server Action IDs remaining secret. In addition, the upstream fix is available in Next.js 15.5.21 and 16.2.11, and upgrading to a fixed version removes the exposure.
Source: Red Hat security advisory for CVE-2026-64643 (CC BY 4.0)

Frequently Asked Questions

Next.js is a React framework for building full-stack web applications. In versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, 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 and Server Actions. By itself, this disclosure is typically a recon/enum
O3 Security · Impact-Aware SCA

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CVE-2026-64643: next — Fixed in 15.5.21