CVE-2026-42211

React Router's vendored turbo-stream v2 allows arbitrary constructor invocation via TYPE_ERROR deserialization leading to Unauth RCE

Description

When using React Router v7 in Framework Mode, there exists a combination of steps that could potentially allow unauthorized RCE through external requests. This first requires the application code to have an existing prototype pollution vulnerability. This can be leveraged into a 2-step attack in which the second step can trigger unauthorized RCE on the remote server.

[!NOTE] This does not impact your React Router application if you are using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).

Patch Available

Fix available through Seal Security. No upgrade required, protect your application instantly.

Fix without upgrading

Score

8.1

Severity

High

Ecosystem

JavaScript

Publish Date

June 3, 2026

Modified Date

June 9, 2026

Score Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected Versions