CVE-2026-39371: RedwoodSDK has a CSRF vulnerability in server function dispatch via GET requests

Summary

Server functions exported from "use server" files could be invoked via GET requests, bypassing their intended HTTP method. In cookie-authenticated applications, this allowed cross-site GET navigations to trigger state-changing functions, because browsers send SameSite=Lax cookies on top-level GET requests.

This affected all server functions – both serverAction() handlers and bare exported functions in "use server" files.

Impact

An attacker could construct a URL containing a known action ID and JSON-encoded arguments. When a victim with an active session visited or was redirected to this URL, the function executed with the victim’s credentials. This affected any server function that performs state-changing operations (writes, deletes, mutations) in applications using cookie-based authentication.

Remediation

Update to rwsdk 1.0.6. No application code changes are required.

The fix enforces the declared HTTP method at dispatch time. GET requests to server functions that require POST now return 405 Method Not Allowed.