CVE-2026-39371

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.

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

CVE-2026-39371 has a CVSS score of 8.1 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.6); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-39371? CVE-2026-39371 is a high-severity cross-site request forgery (CSRF) vulnerability in rwsdk (npm), affecting versions >= 1.0.0-beta.50, <= 1.0.5. It is fixed in 1.0.6. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
2. How severe is CVE-2026-39371? CVE-2026-39371 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of rwsdk are affected by CVE-2026-39371? rwsdk (npm) versions >= 1.0.0-beta.50, <= 1.0.5 is affected.
4. Is there a fix for CVE-2026-39371? Yes. CVE-2026-39371 is fixed in 1.0.6. Upgrade to this version or later.
5. Is CVE-2026-39371 exploitable, and should I be worried? Whether CVE-2026-39371 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
6. What actually determines whether CVE-2026-39371 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.
7. How do I fix CVE-2026-39371? Upgrade rwsdk to 1.0.6 or later.