React Router allows pre-render data spoofing on React-Router framework modeGHSA-cpj6-fhp6-mr6j
HIGHFix: remix-run/react-router@c843029GHSA-cpj6-fhp6-mr6j is a high-severity (CVSS 8.2) CWE-345 vulnerability in react-router. A fix is available for react-router — see the affected versions and patch details below.
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for GHSA-cpj6-fhp6-mr6j.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
react-routernpmDescription
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"
- 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) - 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:
- Send your request by adding the
X-React-Router-Prerender-Dataheader with the previously retrieved object as its value. You can change any value of yourdataobject (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_)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | react-router | ≥ 7.0.0-pre.0&&< 7.5.2 | 7.5.2npm install react-router@7.5.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for react-router, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update react-router to 7.5.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-cpj6-fhp6-mr6j is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
The severity of this vulnerability is rated Moderate, as it does not impact system availability. The effects are confined to the application layer, specifically involving data manipulation and potential cache poisoning, without compromising the underlying system stability.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for GHSA-cpj6-fhp6-mr6j (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift AI 2.23 | rhoai/odh-dashboard-rhel9:v2.23.0-1754417509 | RHSA-2025:13904 |
Frequently Asked Questions
Is GHSA-cpj6-fhp6-mr6j in your dependencies?
Find it across npm, including transitive dependencies.