CVE-2025-43865 – react-router

Package

Manager: npm
Name: react-router
Vulnerable Version: >=7.0 <7.5.2

Severity

Level: High

CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H

CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N

EPSS: 0.00047 pctl0.13773

Details

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](https://github.com/remix-run/react-router/blob/e6c53a0130559b4a9bd47f9cf76ea5b08a69868a/packages/react-router/lib/server-runtime/routes.ts#L87) : <img width="776" alt="Capture d’écran 2025-04-07 à 05 36 58" src="https://github.com/user-attachments/assets/c95b0b33-15ce-4d30-9f5e-b10525dd6ab4" /> 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:  4. 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_)

Metadata

Created: 2025-04-24T16:31:32Z
Modified: 2025-04-25T14:34:15Z
Source: https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2025/04/GHSA-cpj6-fhp6-mr6j/GHSA-cpj6-fhp6-mr6j.json
CWE IDs: ["CWE-345"]
Alternative ID: GHSA-cpj6-fhp6-mr6j
Finding: F204
Auto approve: 1