React Router vulnerable to Denial of Service via reflected user input in single-fetch

Exploitation

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

CVSS

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

EPSS

• CVE-2026-34077: 0.29% estimated exploitation activity in the next 30 days; percentile 22.14 (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.

A DoS vulnerability exists in the React Router v7 Framework Mode, as well as Remix v2.9.0+ with Single Fetch enabled. In some scenarios the underlying serialization algorithm can become a bottleneck when encoding specific types of data into server responses. Please upgrade to React Router v7.14.0 or later. [!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

4 Jun 2026, 15:23 UTC

Last modified by the source

4 Jun 2026, 15:41 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-rxv8-25v2-qmq8

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-rxv8-25v2-qmq8

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# Patch Next advisory brief: CVE-2026-34077

Advisory: React Router vulnerable to Denial of Service via reflected user input in single-fetch
IDs: CVE-2026-34077, GHSA-rxv8-25v2-qmq8
Record: https://patchnext.com/advisories/cve-2026-34077 (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 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: react-router 7.14.0; turbo-stream 3.0.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm react-router: affected >= 7.0.0, < 7.14.0; fixed in 7.14.0
- npm turbo-stream: affected < 3.0.0; fixed in 3.0.0

## 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`.
- `npm ls turbo-stream --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, turbo-stream.
- 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-rxv8-25v2-qmq8 (OSV record GHSA-rxv8-25v2-qmq8 lists affected ranges: npm react-router >=7.0.0 =0 <3.0.0 (fixed))
- Verified: https://github.com/advisories/GHSA-rxv8-25v2-qmq8 (GitHub-reviewed advisory GHSA-rxv8-25v2-qmq8 lists affected ranges: npm react-router >=7.0.0 =0 <3.0.0)

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