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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-42211: 0.42% estimated exploitation activity in the next 30 days; percentile 35.97 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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).

Published by the source

3 Jun 2026, 21:03 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-49rj-9fvp-4h2h

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-49rj-9fvp-4h2h

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# Patch Next advisory brief: CVE-2026-42211

Advisory: React Router's vendored turbo-stream v2 allows arbitrary constructor invocation via TYPE_ERROR deserialization leading to Unauth RCE
IDs: CVE-2026-42211, GHSA-49rj-9fvp-4h2h
Record: https://patchnext.com/advisories/cve-2026-42211 (revision 2, source checked 26 Oct 2026, 12:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: react-router 7.14.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm react-router: affected >= 7.0.0, <= 7.14.1; fixed in 7.14.2

## Suggested inspection (read-only)
- `npm ls react-router --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on react-router.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-49rj-9fvp-4h2h (OSV record GHSA-49rj-9fvp-4h2h lists affected ranges: npm react-router >=7.0.0 <7.14.2 (fixed))
- Verified: https://github.com/advisories/GHSA-49rj-9fvp-4h2h (GitHub-reviewed advisory GHSA-49rj-9fvp-4h2h lists affected ranges: npm react-router >=7.0.0 <=7.14.1)

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