CVE-2026-64645

Next.js: Server-Side Request Forgery in rewrites via attacker-controlled destination hostname

Workarounds

If you cannot upgrade immediately, do not build the hostname of an external rewrites() or redirects() destination from user-controlled input. If a dynamic subdomain is required, constrain the value to hostname-safe characters: value: '(?<region>[a-z0-9-]+)'.

A rewrites() or redirects() rule that builds its external destination hostname from request-controlled input can be pointed at an arbitrary hostname, regardless of the rule's hostname suffix. For a rewrite, Next.js proxies the request to that arbitrary host and serves the response from the application's origin, leading to Server-Side Request forgery. A redirects() rule configured this way is vulnerable to an Open Redirect.

This affects any destination that puts a dynamic segment in the hostname, whether from the path:

// next.config.js
module.exports = {
  async rewrites() {
    return [
      {
        source: '/:tenant',
        destination: 'https://:tenant.api.example.com',
      },
    ]
  },
}

or from a has capture:

// next.config.js
module.exports = {
  async rewrites() {
    return [
      {
        source: '/',
        has: [{ type: 'query', key: 'region', value: '(?<region>.+)' }],
        destination: 'https://:region.api.example.com',
      },
    ]
  },
}

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

Kodem intelligence

Already deployed Kodem?

1. What is CVE-2026-64645? CVE-2026-64645 is a high-severity server-side request forgery (SSRF) vulnerability in next (npm), affecting versions >= 12.0.0, < 15.5.21. It is fixed in 15.5.21, 16.2.11. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. Which versions of next are affected by CVE-2026-64645? next (npm) versions >= 12.0.0, < 15.5.21 is affected.
3. Is there a fix for CVE-2026-64645? Yes. CVE-2026-64645 is fixed in 15.5.21, 16.2.11. Upgrade to this version or later.
4. Is CVE-2026-64645 exploitable, and should I be worried? Whether CVE-2026-64645 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-64645 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-64645?
   • Upgrade next to 15.5.21 or later
   • Upgrade next to 16.2.11 or later

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