High [CVE-2026-64649] Server-Side Request Forgery via malicious host redirection in Server Actions

Next.js is a React framework for building full-stack web applications. In versions 14.1.1 through 15.5.20 and 16.0.0 through 16.2.10, when a Server Action forwards or redirects a request, an attacker can cause the server to send that outbound request to a malicious host (Server-Side Request Forgery).

This requires the attacker's request to control Host-associated headers. In some configurations, it's also possible to obtain internal values that weaken middleware/proxy authorization.

Applications that use Server Actions are affected when the incoming host header is not fixed to a trusted value. This typically occurs on custom servers, or on deployments not behind a proxy that pins the host.

Managed hosting pins the host upstream and is not affected; next start and standalone output do the same from version 14.2 onward. This issue has been fixed in versions 15.5.21 and 16.2.11.

This can lead to Server-Side Request Forgery (SSRF), where the server is tricked into making requests to an attacker-controlled host. Such an attack could potentially expose internal system information or bypass authorization controls.

This Important Server-Side Request Forgery (SSRF) flaw in Next.js Server Actions allows an attacker to redirect outbound requests to a malicious host.