CVE-2026-53666 React Router: Arbitrary Constructor Injection via deserializeErrors() in React Router SSR Hydration
Attackers can trigger arbitrary constructor execution and outbound requests in React Router SSR apps if specific application code allows error manipulation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-53666?
CVE-2026-53666 is a medium-severity code injection vulnerability in remix-run react-router, published on 27 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
React Router is a router for React. In versions 6.4.0 through 7.17.0, if application code was written in a way that allows attacker-supplied input to overwrite certain aspects of errors caught by the SSR process, then it was possible for an attacker to trigger unexpected constructor execution on the client, which would in turn trigger an outbound network request. This is only possible with very specific (and unlikely) application-layer code. Note that this does not impact an application if it is using Declarative Mode. It only impacts Framework Mode and Data Mode applications that perform manual SSR/hydration. This issue has been fixed in version 7.18.0.
Weakness: CWE-470
Which versions are affected by CVE-2026-53666?
2 open source packages ship an affected version, including react-router. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
react-router npm | From 6.4.0 | 7.18.0 |
react-router npm | From 6.4.0 | 7.18.0 |
Products include Shopify React-Router.
How do I fix CVE-2026-53666?
Upgrade react-router to 7.18.0 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-53666 being exploited?
There is no known exploitation of CVE-2026-53666 in the wild and no public exploit code.
Other vulnerabilities in remix-run react-router
- CVE-2026-55685 React Router: Unauthenticated Denial of Service via Inefficient Route Matching
- 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
Sources
Also known as CLSA-2026-1789159895, CLSA-2026-1792253408, CLSA-2026-1792269434, GHSA-337j-9hxr-rhxg, MINI-v493-wr5j-jmqp, ROOT-APP-NPM-CVE-2026-53666.