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This vulnerability exists in React Router’s Framework Mode and its experimental React Server Components (RSC) mode when handling server-side route actions. In these configurations, POST requests to UI routes that trigger server actions may not be automatically protected by the framework’s built-in CSRF defenses. The system incorrectly trusts that a request coming from a user’s browser with a valid session is intentional. An attacker can exploit this by tricking an authenticated user into visiting a malicious webpage. This page can contain a hidden HTML form that silently submits a forged POST request to the vulnerable React Router endpoint. Because the user’s browser automatically sends their session cookies with the request, the server action executes with the victim’s privileges, leading to unauthorized state changes or data manipulation.
Platform: React Router Remix
Version: Framework Mode
Vulnerability: CSRF in Actions
Severity: Moderate
date: 2026-01-08
Prediction: Patch 2026-01-22
What Undercode Say:
Analytics
`npm list react-router-dom`
`grep -r “action” src/routes/`
`curl -X POST http://localhost:3000/action-route -H “Content-Type: application/x-www-form-urlencoded” -d “malicious=data”`
How Exploit
`
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`fetch(‘https://target.app/api/action’, {method: ‘POST’, credentials: ‘include’, body: JSON.stringify({payload: ‘attacker_controlled’})})`
Protection from this CVE
Use Declarative Mode.
Implement CSRF tokens.
Set SameSite cookies.
Impact
Unauthorized data modification.
Privilege escalation possible.
Session integrity compromised.
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Sources:
Reported By: github.com
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