The server was deserializing untrusted input from the client directly into module+export name lookups, and then invoking whatever the client asked for (without verifying that metadata.name was an own property).

    return moduleExports[metadata.name]

My guess is this won't be the last time we see security fallout from that design choice. Not because React is sloppy, but because it’s trying to solve a problem category that traditionally requires explicitness, not magic.

> A pre-authentication remote code execution vulnerability exists in React Server Components versions 19.0.0, 19.1.0, 19.1.1, and 19.2.0 including the following packages: react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack. The vulnerable code unsafely deserializes payloads from HTTP requests to Server Function endpoints.

React's own words: https://react.dev/blog/2025/12/03/critical-security-vulnerab...

> React Server Functions allow a client to call a function on a server. React provides integration points and tools that frameworks and bundlers use to help React code run on both the client and the server. React translates requests on the client into HTTP requests which are forwarded to a server. On the server, React translates the HTTP request into a function call and returns the needed data to the client.

> An unauthenticated attacker could craft a malicious HTTP request to any Server Function endpoint that, when deserialized by React, achieves remote code execution on the server. Further details of the vulnerability will be provided after the rollout of the fix is complete.

What does server components do so much better than SSR? What minute performance gain is achieved more than client side rendering?

Why won’t they invest more on solving the developer experience that took a nosedive when hooks were introduced? They finally added a compiler, but instead of going the svelte route of handling the entire state, it only adds memoization?

If I can send a direct message to the react team it would be to abandon all their current plans, and work on allowing users to write native JS control flows in their component logic.

sorry for the rant.

https://github.com/facebook/react/commit/bbed0b0ee64b89353a4...

and it looks like its been squashed with some other stuff to hide it or maybe there are other problems as well.

this pattern appears 4 times and looks like it is reducing the functions that are exposed to the 'whitelist'. i presume the modules have dangerous functions in the prototype chain and clients were able to invoke them.

      -  return moduleExports[metadata.name];
      +  if (hasOwnProperty.call(moduleExports, metadata.name)) {
      +    return moduleExports[metadata.name];
      +  }
      +  return (undefined: any);

https://vercel.com/changelog/cve-2025-55182

> Cloudflare WAF proactively protects against React vulnerability

https://blog.cloudflare.com/waf-rules-react-vulnerability/

I guess now we'll see more bots scanning websites for "/_next" path rather than "/wp-content".

mind you react in 2017 paid my rent. now cz of the complexity I refuse to work with react.

I think their time as Javascript thought leaders is past due.

I'm just laughing because I called it when they were in the "random idea x posts" about use server.

They'll fix it, but this was what we were warning about.

edit: downvote if you want, but I'm sorry React thinking they could shoehorn "use server" in and not create huge vulnerabilities was a pipe dream at best. I vote gross negligence because EVERYONE knew this was going to happen.