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"
- Install React-Router with its default configuration in Framework mode (https://reactrouter.com/start/framework/installation)
- Add a simple page using a loader (example:
routes/ssr)
- 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_)
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:
routes/ssr)/ssrin our case) adding the following header: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