How severe is GHSA-cpj6-fhp6-mr6j?

GHSA-cpj6-fhp6-mr6j has a CVSS score of 8.2/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-cpj6-fhp6-mr6j?

GHSA-cpj6-fhp6-mr6j affects the following packages: react-router (npm). Ecosystems affected: npm.

How do I fix GHSA-cpj6-fhp6-mr6j?

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.

How do I detect GHSA-cpj6-fhp6-mr6j in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for react-router. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate GHSA-cpj6-fhp6-mr6j if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against GHSA-cpj6-fhp6-mr6j?

O3 pinpoints whether GHSA-cpj6-fhp6-mr6j is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is GHSA-cpj6-fhp6-mr6j actively exploited in the wild?

No public exploit code has been indexed for GHSA-cpj6-fhp6-mr6j yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-cpj6-fhp6-mr6j?

GHSA-cpj6-fhp6-mr6j has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 50th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-cpj6-fhp6-mr6j?

GHSA-cpj6-fhp6-mr6j is classified as CWE-345 (CWE-345). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-cpj6-fhp6-mr6j published, and has it been updated?

GHSA-cpj6-fhp6-mr6j was published on April 24, 2025 and was last updated on February 3, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

GHSA-cpj6-fhp6-mr6j

HIGH

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

Also known asCVE-2025-43865

Published

Apr 24, 2025

Updated

Feb 3, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk50th percentile+0.45%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.

react-routernpm

49.2Mdownloads / week

Description

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-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):

Capture d’écran 2025-04-07 à 05 56 10

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`react-router`	≥ 7.0.0-pre.0&&< 7.5.2	7.5.2

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for react-router. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-cpj6-fhp6-mr6j is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-cpj6-fhp6-mr6j. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## 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

O3 Security · Impact-Aware SCA

Is GHSA-cpj6-fhp6-mr6j in your dependencies?

O3 detects GHSA-cpj6-fhp6-mr6j across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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