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](https://reactrouter.com/start/modes#framework), as well as Remix v2.9.0+ with [Single Fetch](https://v2.remix.run/docs/guides/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](https://reactrouter.com/start/modes#declarative) (`<BrowserRouter>`) or [Data Mode](https://reactrouter.com/start/modes#data) (`createBrowserRouter`/`<RouterProvider>`).
How to fix CVE-2026-34077
To remediate CVE-2026-34077, upgrade the affected package to a fixed version below.
- —upgrade to 7.14.0 or later
- —upgrade to 3.0.0 or later
Is CVE-2026-34077 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-34077.
Affected packages (2)
- >= 7.0.0, < 7.14.0
- from 0, < 3.0.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |