React Router is a router for React. Starting in version 7.2.0 and prior to version 7.5.2, it is possible to force an application to switch to SPA mode by adding a header to the request. If the application uses SSR and is forced to switch to SPA, this causes an error that completely corrupts the page. If a cache system is in place, this allows the response containing the error to be cached, resulting in a cache poisoning that strongly impacts the availability of the application. This issue has been patched in version 7.5.2.
https://github.com/remix-run/react-router/security/advisories/GHSA-f46r-rw29-r322
https://github.com/remix-run/react-router/commit/c84302972a152d851cf5dd859ff332b354b70111