# CVE-2026-64641: Vercel Next.js denial of service in App Router Server Actions

Source: https://junglewise.ai/threats/cve-2026-64641-vercel-next-js-denial-of-service-in-app-router-server-actions  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-27. Updated: 2026-07-27  
License: CC BY 4.0 with a link back

CVE-2026-64641 · Severity: high · CVSS 4 · Published 2026-07-27

Next.js is a popular framework used to build and host web applications. A vulnerability in how the framework handles specific web requests can allow an attacker to overwhelm the server's processor. This results in a denial-of-service condition where the website becomes unresponsive to legitimate users, potentially causing business downtime and operational disruption.

Technologies: [next (npm)](https://junglewise.ai/threats/technologies/npm-next), [Vercel Next.js](https://junglewise.ai/threats/technologies/next-js). Vendors: [npm](https://junglewise.ai/threats/vendors/npm), [Vercel](https://junglewise.ai/threats/vendors/vercel).

## Quick answers

**Is CVE-2026-64641 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-64641 being exploited in the wild.

**How severe is CVE-2026-64641?** High severity, with a CVSS score of 4, published 27 July 2026.

**Which products and versions are affected?** next (npm) SEMVER:introduced=13.0.0,fixed=15.5.21; Vercel Next.js >= 13.0.0, < 15.5.21; >= 16.0.0, < 16.2.11, 13.0.0 - 15.5.20, 16.0.0 - 16.2.10.

**Is there a fix for CVE-2026-64641?** Yes. next (npm): upgrade to 15.5.21 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-64641 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-64641?** Check whether you run next (npm) or Vercel Next.js at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- next (npm): upgrade to 15.5.21 or later

  ```sh
  npm install next@15.5.21
  ```


## Technical details

A denial of service (DoS) vulnerability exists in Next.js due to excessive iteration (CWE-834) when processing crafted requests. The issue resides in the App Router component when at least one Server Action is defined. An unauthenticated remote attacker can send specially crafted requests that trigger high CPU utilization, blocking the event loop and preventing the process from handling subsequent requests. The vulnerability affects versions 13.0.0 through 15.5.20 and 16.0.0 through 16.2.10. It has been remediated in versions 15.5.21 and 16.2.11 by improving the validation performance of Multi-Page Application (MPA) form submissions.

## Affected products

- Vercel Next.js 13.0.0 - 15.5.20, 16.0.0 - 16.2.10

## Identifiers

- CVE-2026-64641
- GHSA-m99w-x7hq-7vfj

## Timeline

- 2026-07-21: patched: Fixes released in v15.5.21 and v16.2.11
- 2026-07-21: advisory: GitHub Security Advisory GHSA-m99w-x7hq-7vfj published
- 2026-07-27: disclosed: CVE-2026-64641 published to NVD

## References

- [https://github.com/vercel/next.js/commit/019628571641dec57aaf349ba0c360e3964e6f12](https://github.com/vercel/next.js/commit/019628571641dec57aaf349ba0c360e3964e6f12)
- [https://github.com/vercel/next.js/pull/96013](https://github.com/vercel/next.js/pull/96013)
- [https://github.com/vercel/next.js/releases/tag/v15.5.21](https://github.com/vercel/next.js/releases/tag/v15.5.21)
- [https://github.com/vercel/next.js/releases/tag/v16.2.11](https://github.com/vercel/next.js/releases/tag/v16.2.11)
- [https://github.com/vercel/next.js/security/advisories/GHSA-m99w-x7hq-7vfj](https://github.com/vercel/next.js/security/advisories/GHSA-m99w-x7hq-7vfj)

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- [Next.js denial of service in App Router with Server Actions](https://junglewise.ai/threats/cve-2026-94482-next-js-denial-of-service-in-app-router-using-server-actions)
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