NodeJS/react-router/7.3.0-pre.1

React Router allows pre-render data spoofing on React-Router framework mode

Summary

After some research, it turns out that it's possible to modify pre-rendered data by adding a header to the request. This allows to completely spoof its contents and modify all the values ​​of the data object passed to the HTML. Latest versions are impacted.

Details

The vulnerable header is X-React-Router-Prerender-Data, a specific JSON object must be passed to it in order for the spoofing to be successful as we will see shortly. Here is the vulnerable code :

To use the header, React-router must be used in Framework mode, and for the attack to be possible the target page must use a loader.

Steps to reproduce

Versions used for our PoC: - @react-router/node: ^7.5.0, - @react-router/serve: ^7.5.0, - react: ^19.0.0 - react-dom: ^19.0.0 - react-router: ^7.5.0

1. Install React-Router with its default configuration in Framework mode (https://reactrouter.com/start/framework/installation)
2. Add a simple page using a loader (example: routes/ssr)
3. Access your page (which uses the loader) by suffixing it with .data. In our case the page is called /ssr:

We access it by adding the suffix .data and retrieve the data object, needed for the header:

1. Send your request by adding the X-React-Router-Prerender-Data header with the previously retrieved object as its value. You can change any value of your data object (do not touch the other values, the latter being necessary for the object to be processed correctly and not throw an error):

As you can see, all values ​​have been changed/overwritten by the values ​​provided via the header.

Impact

The impact is significant, if a cache system is in place, it is possible to poison a response in which all of the data transmitted via a loader would be altered by an attacker allowing him to take control of the content of the page and modify it as he wishes via a cache-poisoning attack. This can lead to several types of attacks including potential stored XSS depending on the context in which the data is injected and/or how the data is used on the client-side.

Credits

• Rachid Allam (zhero;)
• Yasser Allam (inzo_)

React Router allows a DoS via cache poisoning by forcing SPA mode

Summary

After some research, it turns out that 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.

Details

The vulnerable header is X-React-Router-SPA-Mode; adding it to a request sent to a page/endpoint using a loader throws an error. Here is the vulnerable code :

To use the header, React-router must be used in Framework mode, and for the attack to be possible the target page must use a loader.

Steps to reproduce

Versions used for our PoC: - @react-router/node: ^7.5.0, - @react-router/serve: ^7.5.0, - react: ^19.0.0 - react-dom: ^19.0.0 - react-router: ^7.5.0

1. Install React-Router with its default configuration in Framework mode (https://reactrouter.com/start/framework/installation)
2. Add a simple page using a loader (example: routes/ssr)

1. Send a request to the endpoint using the loader (/ssr in our case) adding the following header: X-React-Router-SPA-Mode: yes

Notice the difference between a request with and without the header;

Normal request

With the header

Impact

If a system cache is in place, it is possible to poison the response by completely altering its content (by an error message), strongly impacting its availability, making the latter impractical via a cache-poisoning attack.

Credits

• Rachid Allam (zhero;)
• Yasser Allam (inzo_)