CVE-2026-64646: Vercel Next.js denial of service in Server Actions Edge runtime

CVE-2026-64646 · Severity: medium · CVSS 4 · Published 2026-07-27

Next.js is a popular React-based web framework used to build modern web applications. When Server Actions (a feature for handling form submissions and backend calls) are deployed to Vercel's Edge runtime without proper payload limits, attackers can send oversized requests that consume excessive memory and crash the application. This can disrupt service availability for legitimate users. Administrators can mitigate this by configuring their hosting provider to limit request body size to 5 MiB or less.

Technologies: Vercel Next.js. Vendors: Vercel.

Quick answers

Is CVE-2026-64646 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-64646 being exploited in the wild.
How severe is CVE-2026-64646?
Medium severity, with a CVSS score of 4, published 27 July 2026.
Which products and versions are affected?
Vercel Next.js >= 13.0.0, < 15.5.21; >= 16.0.0, < 16.2.11, >=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-2026-64646?
A patch was published on 2026-07-21: Patches committed for Next.js 15.5.21 and 16.2.11 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-64646 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-64646?
Check whether you run 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.

Technical details

This vulnerability (CWE-770) stems from a lack of request body size validation in Next.js Server Actions when running on the Edge runtime. Server Actions in the App Router did not enforce a default limit on incoming request payload size, allowing an attacker to send arbitrarily large POST requests that cause the serverless function to allocate excessive memory until it becomes resource-exhausted and unavailable. The attack requires network access and no authentication or special privileges; no user interaction is required. The fix, deployed in versions 15.5.21 and 16.2.11, introduces a configurable `serverActions.bodySizeLimit` setting that defaults to 1 MB, preventing memory exhaustion attacks. Administrators unable to upgrade should configure their hosting environment to reject requests exceeding ~5 MiB.

Affected products

  • Vercel Next.js >=13.0.0 <15.5.21, >=16.0.0 <16.2.11

Identifiers

  • CVE-2026-64646
  • GHSA-4c39-4ccg-62r3

Timeline

  • 2026-07-22: disclosed: Advisory published by Vercel
  • 2026-07-21: patched: Patches committed for Next.js 15.5.21 and 16.2.11

References

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