CVE-2026-55685 React Router: Unauthenticated Denial of Service via Inefficient Route Matching
Unauthenticated attackers can cause denial of service via inefficient route matching in the manifest endpoint, affecting server-side rendering applications.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55685?
CVE-2026-55685 is a high-severity denial of service vulnerability in remix-run react-router, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
React Router is a router for React. In versions 7.0.0 through 7.17.0, the manifest endpoint could be accessed via unauthenticated targeted requests that would put heavy load on the server and slow down response times. This issue is a follow up to CVE-2026-42342, and does not does not impact React Router applications using Declarative Mode (<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>). This issue has been fixed in version 7.18.0.
Which versions are affected by CVE-2026-55685?
2 open source packages ship an affected version, including react-router. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
react-router npm | From 7.0.0 | 7.18.0 |
react-router npm | From 7.0.0 | 7.18.0 |
Products include Shopify React-Router.
How do I fix CVE-2026-55685?
Upgrade react-router to 7.18.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-55685 being exploited?
There is no known exploitation of CVE-2026-55685 in the wild and no public exploit code.
Other vulnerabilities in remix-run react-router
- CVE-2026-21884 React Router SSR XSS in ScrollRestoration
- CVE-2026-42211 React Router's vendored turbo-stream v2 allows arbitrary constructor invocation via TYPE_ERROR deserialization leading to Unauth RCE
- CVE-2026-33245 React Router vulnerable to XSS in unstable RSC redirect handling via javascript: redirect targets
- CVE-2026-22029 React Router vulnerable to XSS via Open Redirects
- CVE-2025-59057 React Router has XSS Vulnerability
Sources
Also known as CLSA-2026-1784856417, CLSA-2026-1792139276, CLSA-2026-1792253398, CLSA-2026-1792253415, CLSA-2026-1792419113, CLSA-2026-1792419191 and 10 more.