CVE-2026-34077

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

Description

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>).

Patch Available

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

Fix without upgrading

Score

7.5

Severity

High

Ecosystem

JavaScript

Publish Date

June 4, 2026

Modified Date

June 4, 2026

Score Vector

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

Affected Versions