Denial of service and source code exposure in React Server Components

https://react.dev/blog/2025/12/11/denial-of-service-and-source-code-exposure-in-react-server-components

by sangeeth96 • 7 months ago

346 225 7 months ago

chuckadams5• 7 months ago

I remember when the point of an SPA was to not have all these elaborate conversations with the server. Just "here's the whole app, now only ask me for raw data."

tshaddox2• 7 months ago

That was indeed one of the main points of SPAs, but React Server Components are generally not used for pure SPAs.

reactordev2• 7 months ago

Correct, their main purpose is ecosystem lock-in. Because why return json when you can return html. Why even build a SPA when the old school model of server-side includes and PHP worked just fine? TS with koa and htmx if you must but server-side react components are kind of a waste of time. Give me one example where server side react components are the answer over a fetch and json or just fetching an html page?

robertoandred3• 7 months ago

Sure they are. Next sites are SPAs.

rustystump2• 7 months ago

It also decoupled fe and backend. You could use the same apis for say mobile, desktop and web. Teams didnt have to cross streams allowing for deeper expertise on each side.

Now they are shoving server rendering into react native…

pjmlp3• 7 months ago

Until they discovered why so many of us have kept with server side rendering, and only as much JS as needed.

Then they rediscovered PHP, Rails, Java EE/Spring, ASP.NET, and reboted SPAs into fullstack frameworks.

sangeeth963• 7 months ago

Then they rediscovered PHP, Rails, Java EE/Spring, ASP.NET, and reboted SPAs into fullstack frameworks.

I can understand the dislike for Next but this is such a poor comparison. If any of those frameworks at any point did half the things React + Next-like frameworks accomplished and the apps/experiences we got since then, we wouldn't be having this discussion.

whizzter• 7 months ago

I sometimes feel like I go on and on about this... but there is a difference between application and pages (even if blurry at times), and Next is a result of people doing pages adopting React that was designed for applications when they shouldn't have.

hedayet2• 7 months ago

I'd be interested in adopting a sole-purpose framework like that.

moomoo11• 7 months ago

I think people just never understood SPA.

Like with almost everything people then shit on something they don’t understand.

_jzlw2• 7 months ago

It's funny (in a "wtf" sort of way) how in C# right now, the new hotness Microsoft is pushing is Blazor Server, which is basically old-school .aspx Web Forms but with websockets instead of full page reloads.

Every action, every button click, basically every input is sent to the server, and the changed dom is sent back to the client. And we're all just supposed to act like this isn't absolutely insane.

c0balt• 7 months ago

Hotwire et al are also doing part of this. It isn't a new concept but it seems to come and go it terms of popularity

McGlockenshire• 7 months ago

And we're all just supposed to act like this isn't absolutely insane.

This is insane to you only if you didn't experience the emergence of this technique 20-25 years ago. Almost all server-side templates were already partials of some sort in almost all the server-side environments, so why not just send the filled in partial?

Business logic belongs on the server, not the client. Never the client. The instant you start having to make the client smart enough to think about business logic, you are doomed.

CharlieDigital• 7 months ago

It's kinda nice.

Main downside is the hot reload is not nearly as nice as TS.

But the coding experience with a C# BE/stack is really nice for admin/internal tools.

vbezhenar• 7 months ago

I saw this kind of interactivity in Apache Wicket Java framework. It's very interesting approach.

seer2• 7 months ago

Isn’t that what Phoenix (Elixir) is? All server side, small js lib for partial loads, each individual website user gets their own thread on the backend with its own state and everything is tied together with websockets.

Basically you write only backend code, with all the tools available there, and a thin library makes sure to stich the user input to your backend functions and output to the front end code.

Honestly it is kinda nice.

JeremyNT• 7 months ago

Well, maybe it isn't so insane?

Server side rendering has been with us since the beginning, and it still works great.

Client side page manipulation has its place in the world, but there's nothing wrong with the server sending page fragments, especially when you can work with a nice tech stack on the backend to generate it.

oefrha• 7 months ago

Yes, I say this every time this topic comes up: it took many years to finally have mainstream adoption of client-side interactivity so that things are finally mostly usable on high latency/lossy connections, but now people who’re always on 10ms connections are trying to snatch that away so that entirely local interactions like expanding/collapsing some panels are fucked up the moment a WebSocket is disconnected. Plus nice and simple stateless servers now need to hold all those long-lived connections. WTF. (Before you tell me about Alpine.js, have you actually tried mutating state on both client and server? I have with Phoenix and it sucks.)

array_key_first4• 7 months ago

This is how client-server applications have been done for decades, it's basically only the browser that does the whole "big ole requests" thing.

The problem with API + frontend is:

1. You have two applications you have to ensure are always in sync and consistent.

2. Code is duplicated.

3. Velocity decreases because in order to implement almost anything, you need buy-in from the backend AND frontend team(s).

The idea of Blazor Server or Phoenix live view is "the server runs the show". There's now one source of truth, and you don't have to spend time making sure it's consistent.

I would say, really, 80% of bugs in web applications come from the client and server being out of sync. Even if you think about vulnerability like unauthorized access, it's usually just this. If you can eliminate those 80% or mitigate them, then that's huge.

Oh, and thats not even touching on the performance implications. APIs can be performant, but they usually aren't. Usually adding or editing an API is treated as such a high risk activity that people just don't do it - so instead they contort, like, 10 API calls together and discard 99% of the data to get the thing they want on the frontend.

tracker1• 7 months ago

Yeah, I kind of hate it... Blazor has a massive payload and/or you're waiting seconds to see a response to a click event. I'm not fond of RSC either... and I say this as someone absolutely and more than happy with React, Redux and MUI for a long while at this point.

I've been loosely following the Rust equivalents (Leptos, Yew, Dioxux) for a while in the hopes that one of them would see a component library near the level of Mantine or MUI (Leptos + Thaw is pretty close). It feels a little safer in the longer term than Blazor IMO and again, RSC for react feels icky at best.

epolanski2• 7 months ago

Yeah, but then people started building bloated static websites with those libraries instead of using a saner template engine + javascript approach which is fast, easy to cache, debug, and has stellar performance and SEO.

Little it helped that even React developers were saying that it was the wrong tool for plenty use cases.

Worst of all?

The entire nuance of choosing the right tool for the job has been long lost on most developers. Even the comments I read on HN make me question where the engineering part of the job starts.

CodingJeebus2• 7 months ago

It also doesn't help that non-technical stakeholders sometimes want a say in a tech stack conversation as well. I've been at more than one company where either the product team or the acquiring firm wanted us to migrate away from a tried and true Rails setup to a fullstack JS platform simply because they either wanted the UI development flexibility or to not have to hire Ruby devs.

Non-technical MBA's seem to have a hard time grasping that a JS-only platform is not a panacea and comes with serious tradeoffs.

rikafurude21• 7 months ago

Im confused, did the update from last week for the RCE bug also include fixes for these new CVEs or will I need to update again? npm audit says theres no issues

billywhizz• 7 months ago

is it not obvious?

These issues are present in the patches published last week.
The patches published last week are vulnerable.
If you already updated for the Critical Security Vulnerability, you will need to update again.

rickhanlonii5• 7 months ago

GitHub has to review the advisories and publish it for it to show in `npm audit`, so it's delayed.

theogravity• 7 months ago

You need to update again.

cluckindan2• 7 months ago

This could be the Next.js motto.

qingcharles2• 7 months ago

My Umami stats box got "pwned" about 15 mins after the last CVE was published and I spent an hour or so cleaning up that mess and upgrading everything. Not looking forward to doing it again today.

ChrisArchitect• 7 months ago

React2Shell and related RSC vulnerabilities threat brief - Cloudflare

https://blog.cloudflare.com/react2shell-rsc-vulnerabilities-... (https://news.ycombinator.com/item?id=46237515)

sangeeth963• 7 months ago

Next team just published this: https://nextjs.org/blog/security-update-2025-12-11

Seems to affect 14.x, 15.x and 16.x.

carlcortright• 7 months ago

dammit

tagraves2• 7 months ago

It's really concerning that the biggest, most eye-grabbing part of this posting is the note with the following: "It’s common for critical CVEs to uncover follow‑up vulnerabilities."

Trying to justify the CVE before fully explaining the scope of the CVE, who is affected, or how to mitigate it -- yikes.

treesknees2• 7 months ago

What’s concerning about it? The first thing I thought when I read the headline was “wow, another react CVE?” It’s not a justification, it’s an explanation to the most obvious immediate question.

vcarl• 7 months ago

It's definitely a defensive statement, proactively covering the situation as "normal". Normal it may be, but emphasizing that in the limited space of a tweet thread definitely indicates where their mind is on this, I'd think.

tom13372• 7 months ago

But it is another React CVE. Doesn't really matter why it was uncovered, it's bad that it existed either way

brazukadev8• 7 months ago

an insecure software will have multiple CVEs, not necessarily related to each other. Those 3 are probably not the only ones.

zwnow• 7 months ago

Welcome to the React, Next, Vercel ecosystem. Our tech may be shite but we look fancy.

brazukadev8• 7 months ago

The Vercel CEO post congratulating his team for how they managed the vulnerability was funny

samdoesnothing2• 7 months ago

Also kind of funny that they're comparing it to Log2Shell. Maybe not the best sort of company to be keeping...

everfrustrated• 7 months ago

React is the new JavaBean

haileys• 7 months ago

Perception management

https://en.wikipedia.org/wiki/Perception_management

rickhanlonii5• 7 months ago

Thanks for the feedback, I adjusted it here so the first note is related to the impacted versions:

https://github.com/reactjs/react.dev/pull/8195

tagraves2• 7 months ago

I appreciate the follow up! I think it looks great now and doesn’t read as defensively anymore!

hitekker• 7 months ago

There are a lot of careers riding on the optics here.

IceDane2• 7 months ago

No, there aren't. The react team isn't going to axe half the team because there's a high severity CVE.

TZubiri7• 7 months ago

Very standard in security, announcements always always always try to downplay their severity.

rickhanlonii5• 7 months ago

fwiw, the goal here wasn't to downplay the severity, but to explain the context to an audience who might not be familiar with CVEs and what's considered normal. I moved the note down so the more important information like severity, impacted versions, and upgrade instructions are first.

0xblinq3• 7 months ago

I think the same. To me it looks like a Vercel marketing employee wrote that.

rickhanlonii5• 7 months ago

After Log4Shell, additional CVEs were reported as well.

It’s common for critical CVEs to uncover follow‑up vulnerabilities because researchers scrutinize adjacent code paths looking for variant exploit techniques to test whether the initial mitigation can be bypassed.

PKop• 7 months ago

The vulnerabilities existing is not a consequence of previous CVEs so this seems like an irrelevant non sequitur to keep mentioning everywhere.

bflesch• 7 months ago

So we have a new React CVE and tomorrow is Friday, so please be prepared for a new outage brought to you by the super-engineers at Cloudflare.

venturecruelty• 7 months ago

Look on the bright side: maybe GitHub will be down first, so nobody can upload any vulnerable code right before the weekend.

simonw• 7 months ago

React Server Components always felt uncomfortable to me because they make it hard to look at a piece of JavaScript code and derive which parts of it are going to run on the client and which parts will run on the server.

It turns out this introduces another problem too: in order to get that to work you need to implement some kind of DEEP serialization RPC mechanism - which is kind of opaque to the developer and, as we've recently seen, is a risky spot in terms of potential security vulnerabilities.

tom13372• 7 months ago

I was a fan of NextJS in the pages router era. You knew exactly where the line was between server and client code and it was pretty easy to keep track of that. Then I've began a new project and wanted to try out app router and I hated it. So many (to me common things) where just not possible because the code can run in the client and on the server so Headers might not always be available and it was just pure confusion whats running where.

dawnerd• 7 months ago

I pretty much dumped a side project that was using next over the new router. It's so much more convoluted, way too many limitations. Who even really wants to make database queries in front end code? That's sketchy as heck.

Uehreka• 7 months ago

I think we (the Next.js user community) need to organize and either convince Vercel to announce official support of the Pages router forever (or at least indefinitely, and stop posturing it as a deprecated-ish thing), or else fork Next.js and maintain the stable version of it that so many of us enjoyed. Every time Next comes up I see a ton of comments like this, everyone I talk to says this, and I almost never hear anyone say they like the App Router (and this is a pretty contrarian site, so if they existed I’d expect to see them here).

ashishb6• 7 months ago

This happens in Next.js as well https://github.com/vercel/next.js/discussions/11106

sangeeth963• 7 months ago

This is what I asked my small dev team after I recently joined and saw that we were using Next for the product — do we know how this works? Do we have even a partial mental model of what's happening? The answers were sadly, pretty obvious. It was hard enough to get people to understand how hooks worked when they were introduced, but the newer Next versions seem even more difficult to grok.

I do respect the things React + Next team is trying to accomplish and it does feel like magic when it works but I find myself caring more and more about predictability when working with a team and with every major version of Next + React, that aspect seems to be drifting further and further away.

stack_framer2• 7 months ago

I feel the same. In fact, I'll soon be preparing a lunch and learn on trying out Solid.js. I'm hoping to convince the team that we should at least try a different mental model and see if we like it.

TZubiri7• 7 months ago

I had this issue with a React app I inherited, there was a .env with credentials, and I couldn't figure out whether it was being read from the frontend or the backend.

So I ran a static analysis (grep) on the apk generated and

points light at face dramatically

the credentials were inside the frontend!

jaredwiener• 7 months ago

Why would you have anything for the backend in an APK? Wouldnt that be an app, that by definition runs on the client?

Most frameworks also by default block ALL environment variables on the client side unless the name is preceded by something specific, like NEXT_PUBLIC_*

lmm2• 7 months ago

Yeah. Being able to write code that's polymorphic between server and client is great, but it needs to be explicit and checked rather than invisible and magic. I see an analogy with e.g. code that can operate on many different types: it's a great feature, but really you want a generics feature where you can control which types which pieces of code operate on, not a completely untyped language.

danabramov4• 7 months ago

It is explicit and checked.

You have two poison pills (`import "server-only"` and `import "client-only"`) that cause a build error when transitively imported from the wrong environment. This lets you, for example, constrain that a database layer or an env file can never make it into the client bundle (or that some logic that requires client state can never be accidentally used from the stateless request/response cycle). You also have two directives that explicitly expose entry points between the two worlds.

The vulnerabilities in question aren't about wrong code/data getting pulled into a wrong environment. They're about weaknesses in the (de)serialization protocol which relied on dynamic nature of JavaScript (shared prototypes being writable, function having a string constructor, etc) to trick the server into executing code or looping. These are bad, yes, but they're not due to the client/server split being implicit. They're in the space of (de)serialization.

jaredklewis• 7 months ago

I do think RSC and server side rendering in general was over adopted.

Have a Landing/marketing page? Then, yes, by all means render on the server (or better yet statically render to html files) so you squeeze every last millisecond you can out of that FCP. Also easy to see the appeal for ecommerce or social media sites like facebook, medium, and so on. Though these are also use cases that probably benefit the least from React to begin with.

But for the "app" part of most online platforms, it's like, who cares? The time to load the JS bundle is a one time cost. If loading your SaaS dashboard after first login takes 2 seconds versus 3 seconds, who cares? The amount of complexity added by SSR and RSC is immense, I think the payout would have to be much more than it is.

sakesun• 7 months ago

Deeply agree.

joshdavham2• 7 months ago

I'm no javascript framework expert, but how vulnerable do people estimate other frameworks like Angular, Sveltekit and Nuxt to be to this sort of thing? Is React more disposed to be at risk? Is it just because there are more eyes on React due to its popularity?

rk062• 7 months ago

nuxt, sveltekit etc don't have RSC equivalent. and won't have in future either. Vue has discussed it and explicitly rejected it. also RSC was proposed to sveltekit, they also rejected it citing public endpoint should not be hidden

they may get other vulnemerelities as they are also in JS, but RSC class vulelnebereleties won't be there

0xblinq3• 7 months ago

This is why I'm a big advocate of Inertia.js [1]. For me it's the right balance of using "serious" batteries included traditional MVC backends like Laravel, Rails, Adonis, Django, etc... and modern component based frontend tools like React, Vue, Svelte, etc. Responsibilities are clear, working in it is easy, and every single time I used it feels like you're using the right tool for each task.

I can't recommend it enough. If you never tried/learnt about it, check it out. Unless you're building an offline first app, it's 100% the safest way to go in my opinion for 99.9% of projects.

[1] https://inertiajs.com/

tacker20003• 7 months ago

I am also in love with Inertia, it lets you use a React frontend and a Laravel backend without a dedicated API or endpoints, its so much faster to develop and iterate, and you dont need to change your approach or mental model, it just makes total sense.

Instead of creating routes and using fetch() you just pass the data directly to the client side react jsx template, inertia automatically injects the needed data as json into the client page.

tonyhart7• 7 months ago

turns out a separation of concern is valid approach for decades

React team reinvent the wheel again and again and now we back to laravel

dirkc• 7 months ago

I 100% agree. I didn't even bother to think about the security implications - why worry about security implications if the whole things seems like a bad idea?

In retrospect I should have given it more thought since React Server Components are punted in many places!

hedayet2• 7 months ago

I wonder what does these vulnerabilities mean for Facebook. As per my knowledge, Facebook's the biggest web app written in React.

jsheard• 7 months ago

Does Facebook actually use RSC? I thought it was mainly pushed by the Nextjs/Vercel side of the React team.

samdoesnothing2• 7 months ago

No they don't. I think Meta is just big enough that they don't really care what is happening with React anymore haha.

acemarke2• 7 months ago

No, but it's primarily because Meta has their own server infrastructure already. RSCs are essentially the React team trying to generalize the data fetching patterns from Meta's infrastructure into React itself so they can be used more broadly.

I wrote an extensive post and did a conference talk earlier this year recapping the overall development history and intent of RSCs, as best as I understand it from a mostly-external perspective:

- https://blog.isquaredsoftware.com/2025/06/react-community-20...

- https://blog.isquaredsoftware.com/2025/06/presentations-reac...

tacker20003• 7 months ago

This is about React Server Components, a subset/feature of React that can optionally be installed and used.

Apps that use React without server components are not affected.

shadowgovt• 7 months ago

Oh boy, I somehow missed that React was offering these.

Google has a similar technology in-house, and it was a bit of a nightmare a few years back; the necessary steps to get it working correctly required some very delicate dancing.

I assume it's gotten better given time.

aatd862• 7 months ago

LOL. I must have divination powers. I am currently working on a UI framework and opened an issue just 3 weeks ago that says:

***

Seems that server functions are all the rage. We are unlikely to have them.

The main reason is that it ties the frontend and the backend together in undesirable ways.

It forces a js backend upon people (what if I want to use Go for instance).

The api is not client agnostic anymore. How to specify middleware is not clear.

Requires a bundler, so destroys isomorphism (isomorphic code requires no difference between the client and the server/ environment agnostic).

Even if it requires a bundler because it separates client and server implementation files, it blurs the data scoping (especially worrying for sensitive data) Do one thing and do it well: separate frontend and backend.

It might be something that is useful for people who only plan on having a javascript web frontend server separate from the API server that links to the backend service.

Besides, it is really not obvious to me how it becomes architecturally clearer. It would double the work in terms of security wrt authorization etc. This is at least not a generic pattern.

So I'd tend to go opposite to the trend and say no. Who knows, we might revisit it if anything changes in the future.

***

And boy, look at the future 3 weeks later...

To be fair, the one good thing is that they are hardening their implementation thanks to these discoveries. But still seems to me that this is wholly unnecessary and possibly will never be safe enough.

Anyway, not to toot my own horn, I know for a fact these things are difficult. Just found the timing funny. :)

brazukadev8• 7 months ago

I'm curious about your UI framework, is it public?

aatd862• 7 months ago

Not public yet. Under review.

ashishb6• 7 months ago

The JavaScript fanatics will downvote me for saying this, but I'll say this, "using a single JavaScript codebase on your client-side and server-side is like cooking food in your toilet, sooner or later, contamination is guaranteed" [1]

1 - https://ashishb.net/tech/javascript/

leptons2• 7 months ago

This isn't a Javascript problem, this is a React problem. You could theoretically rewrite React and RSC in any language and the outcome would be the same. Say Python ran in the browser natively, and you reimplented React on browser and server in Python. Same problem, not Javascript.

ashishb6• 7 months ago

This isn't a Javascript problem, this is a React problem.

It happened with Next.js as well https://github.com/vercel/next.js/discussions/11106

Say Python ran in the browser natively, and you reimplented React on browser and server in Python. Same problem, not Javascript.

Yes.

And since Python does not natively run in the browser, that mistake never happens. With JavaScript, the desire to have "backend and frontend in a single codebase" requires active resistance.

pier252• 7 months ago

You can still have separate codebases for server and client in JS/TS...

ashishb6• 7 months ago

You can still have separate codebases for server and client in JS/TS...

Indeed, but unlike Go/Python (backend) and TS/JS (frontend), the separation is surmountable, and the push to "reuse" is high.

0xblinq3• 7 months ago

You're mixing programming languages with software architecture.

ashishb6• 7 months ago

You're mixing programming languages with software architecture.

Programming languages do lead to certain software architectures. These are independent but not orthogonal issues.

yread• 7 months ago

Were there not enough eyes on React Server Components before the patches from last week?

Inviz• 7 months ago

have you seen the code of next.js? its completely impenetrable, and the packages have legacy versions of the same files coexisting, it's like huge hairball

manfre• 7 months ago

I've noticed a pattern in the security reports for a project I'm involved in. After a CVE is released, for the next month or so there will likely be additional reports targeting the same (or similar) areas of the framework. There is definitely a competitive spirit amongst security researchers as they try to get more CVEs credited to them (and potentially bounties).

hollowturtle3• 7 months ago

Wouldn't make more sense keeping React smaller and left those features to frameworks? I liked it more when it was marketed as the View in MVC. Surely can still be used like that today but it still feels bloated

ivanjermakov• 7 months ago

git checkout v15.0.0

There we go.

hollowturtle3• 7 months ago

Can I have v15 with the rendering optimizations of further versions?

TZubiri7• 7 months ago

But the react-components are a separate library, they are not installed by default

hollowturtle3• 7 months ago

? afaik react server components made it to core

bitbasher• 7 months ago

I remember when my greatest fear was sql injection. It’s great to see we have become more secure with our technology.

_heimdall• 7 months ago

I do hope this means we can finally stop hearing about RSC. The idea is an interesting solution to problems that never should exist in the first place.

rvz• 7 months ago

React patches one vulnerability and two more are revealed, just like a Hydra.

At this point you might as well deprecate RSC as it is clearly a contraption for someone trying to justify a promotion at Meta.

Maybe they are going to silently remove “Built RSC at Meta!” in their LinkedIn bios after this. So what other vulnerabilities are going to be revealed in React after this one?

marksomnian• 7 months ago

Meta don’t use RSC: https://bsky.app/profile/en-js.bsky.social/post/3lmvwmr5rfs2...

We are not using RSC at Meta yet, bc of limits of our packaging infra (it’s great at different things) and because Relay+GraphQL gives us many of the same benefits as RSCs. But we are fans and users of server driven UI and incrementally working toward RSC.

(as of April 2025)

ginkgotree• 7 months ago

I'm only surprised it took this long for an exposure of backend data to the front end to be discovered in RSC

hbbio2• 7 months ago

We pioneered a lot of things with Opa, 15 years ago now. Opa featured automatic code "splitting" between client and server, introduced the JSX syntax although it wasn't called that way (Jordan at Facebook used Opa before creating React, but the discussions around the syntax happened at W3C notably with another Facebook employee, Tobie).

Since the Opa compiler was implemented in OCaml (we were looking more like Svelte than React as a pure lib), we performed a lot of statical analysis to prevent the wide range of attacks on frontend code (XSS, CSRF, etc.) and backend code. The Opa compiler became a huge beast in part because of that.

In retrospect, better separation of concerns and foregoing completely the idea of automatic code splitting (what React Server Components is) or even having a single app semantics is probably better for the near future. Our vision (way too early), was that we could design a simple language for the semantics and a perfect advanced compiler that would magically output both the client and the server from that specification. Maybe it's still doable with deterministic methods. Maybe LLMs will get to automatic code generation of all parts in one shot before.

danabramov4• 7 months ago

Note that the exploits so far haven’t had much to do with “server code/data getting bundled into the client code” or similar which you’re alluding to. Also, RSC does not try to “guess” how to split code — it is deterministic and always user-controlled.

The vulnerabilities so far were weaknesses in the (de)serializer stemming from the dynamism of JavaScript — ability to hijack root object prototype, ability to toString functions to get their code, ability to override a Promise then implementation, ability to construct a function from a string. The patches are patching the (de)serializer to work around those dynamic pieces of JavaScript to avoid those gaps. This is similar to mistakes in parsers where they’re fooled by properties called hasOwnProperty/constructor/etc.

The serialization format is essentially “JSON with Promises and code chunk references”, and it seems like there’s enough pieces where dynamic nature of JS can leak that needed to be plugged. Hopefully with more scrutiny on the protocol, these will be well-understood by the team. The surface area there isn’t growing much anymore (it’s close to being feature-complete), and the (de)serializers themselves are roughly 5 kloc each.

The problem you had in Opa is solved in RSC with build-time assertions (import "server-only" is the server environment poison pill, and import "client-only" is the client environment poison pill). These poison pills work transitively up the module import stack and are statically enforced and prevent code (eg DB code, secrets, etc) from being pulled into the wrong environment. Of course this doesn’t prevent bugs in the (de)serializer but it’s why the overall approach is sound, in the absence of (de)serialization vulnerabilities.

hbbio2• 7 months ago

The problem we tried to solve with Opa was more general than RSC, probably too general.

    // Opa decides
    function client_or_server (x, y) { ... }
    // Client-side
    client function client_function(x, y) {= }
    // Server-side
    server function server_function(x, y) {... }

Without the optional side inference (which could also use both), it seems we had similar side constraints, and serializers/sanitizers. Probably with the same flaws as the recent vulnerabilities... Like all the OWASP AppSec circa 2013-2015 range of exploits in browser countermeasures when the browsers where starting to roll out defense in depth with string matching :)

Philpax• 7 months ago

You might be interested in Electric Clojure [1], although I must admit that I have not used it myself.

[1] https://github.com/hyperfiddle/electric

yawaramin3• 7 months ago

Ocsigen Eliom did it before Opa, no?

ydj• 7 months ago

I noticed requests that were exploiting the vulnerability were turning into timeouts pretty much immediately after rolling out the patch. I’m surprised it took so long for it to be announced.

greatgib• 7 months ago

In my point of view, this is well deserved to idiots that are seriously using RSC in production, despite that being a very bad idea...

delifue2• 7 months ago

Any attempt that blurs boundary between client and server is unsafe.

delifue2• 7 months ago

React server component is frontend's attempt of "eating" backend.

On the contrary, HTMX is the attempt of backend "eating" frontend.

HTMX preserves the boundary between client and server so it's more safe in backend, but less safe in frontend (risk of XSS).

yawaramin3• 7 months ago

Htmx doesn't really have an XSS problem, this was solved by templating language long ago. See https://htmx.org/essays/web-security-basics-with-htmx/#alway...

jgalt212• 7 months ago

I remember some podcast interview with Miško Hevery talking about how Qwik was very emphatic about what code ran on the server and what ran on the client. Seems self-evident and prescient. It was a great interview as Miško Hevery is extremely articulate about the problems at hand. If I find it, I'll post.

tills13• 7 months ago

Y'all are so pessimistic. React Server Components are great. React is a complex piece of software. Bugs happen.

ipnon• 7 months ago

Personally I prefer simple software without bugs! This security vulnerability highlights a serious issue with React. It’s a SPA framework, a server side framework, and a functional component library all at the same time. And it’s apparently getting so complex that it’s introducing source code exposures.

I’m not interested in flame wars per se, but I can tell you there are better alternatives, and that the closer you stay towards targeting the browser itself the better, because browser APIs are at least an order of magnitude more secure and performant than equivalent JS operations.

WatchDog• 7 months ago

When I looked into RSC last week, I was struck by how complex it was, and how little documentation there seems to be on it.

In fairness react present it as an "experimental" library, although that didn't stop nextjs from widely deploying it.

I suspect there will be many more security issues found in it over the next few weeks.

Nextjs ups the complexity orders of magnitude, I couldn't even figure out how to set any breakpoints on the RSC code within next.

Next vendors most of their dependencies, and they have an enormously complex build system.

The benefits that next and RSC offer, really don't seem to be worth the cost.

firtoz• 7 months ago

People did complain about next exposing "react, not ready for production" things as "the latest and greatest thing from nextjs" for quite a while now

I had moved off nextjs for reasons like these, the mind load was getting too heavy for not too much benefit

mexicocitinluez• 7 months ago

and how little documentation there seems to be on it

DISCLAIMER: After years of using Angular/Ember/Jquery/VanillaJs, jumping into React's functional components made me enjoy building front-ends again (and still remains that way to this very day). That being said:

This has been maybe the biggest issue in React land for the last 5 years at least. And not just for RSC, but across the board.

It took them forever to put out clear guidance on how to start a new React project. They STILL refuse to even acknowledge CRA exist(s/ed). The maintainers have actively fought with library makers on this exact point, over and over and over again.

The new useEffect docs are great, but years late. It'll take another 3-4 years before teh code LLMs spit out even resemble that guidance because of it.

And like sure, in 2020 maybe it didn't make sense to spell out the internals of RSC because it was still in active development. But it's 2025. And people are using it for real things. Either you want people to be successful or you want to put out shiny new toys. Maybe Guillermo needs to stop palling around with war criminals and actually build some shit.

It might be one of the most absurd things about React's team: their constitutional refusal to provide good docs until they're backed into a corner.

kpozin• 7 months ago

A framework designed to blur the line between code running on the client and code running on the server — forgot the distinction between code running on the client and code running on the server. I don't know what they expected.

(The same confusion comes up regularly whenever you touch Next.js apps.)

aabhay• 7 months ago

“use insecure”

dizlexic2• 7 months ago

I'm not going to let go my argument with Dan Abramov on x 3 years ago where he held up rsc as an amazing feature and i told him over and over he was making a foot gun. tahdah!

I'm a nobody PHP dev. He's a brilliant developer. I can't understand why he couldn't see this coming.

peacebeard• 7 months ago

You might be more brilliant than you think.

danabramov4• 7 months ago

For what it’s worth, I’ve just built an app for myself with RSC, and I’m still a huge fan of this way of building and structuring web software.

I agree I underestimated the likelihood of bugs like this in the protocol, though that’s different from most discussions I’ve had about RSC (where concerns were about user code). The protocol itself has a fairly limited surface area (the serializer and deserializer are a few kloc each), and that’s where all of the exploits so far have concentrated.

Vulnerabilities are frustrating, and this seems to be the first time the protocol is getting a very close look from the security community. I wish this was something the team had done proactively. We’ll probably hear more from the team after things stabilize a bit.

brazukadev8• 7 months ago

RSC is not a protocol, that is probably one of the reasons it is bad and affected only NextJS - most other server framework struggled and gave up this mistake that was React Server.

locallost• 7 months ago

I'm not defending React and this feature, and I also don't use it, but when making a statement like that the odds are stacked in your favor. It's much more likely that something's a bad idea than a good idea, just as a baseball player will at best fail just 65-70% of the time at the plate. Saying for every little thing that it's a bad idea will make you right most of the time.

But sometimes, occasionally, a moonshot idea becomes a home run. That's why I dislike cynicism and grizzled veterans for whom nothing will ever work.

dizlexic2• 7 months ago

You're probably right. This one just felt like Groundhog Day, but I can't argue with "nothing ventured nothing gained".

jdkoeck• 7 months ago

A tale as old as time: hubris. A successful system is destined to either stop growing or morph into a monstrosity by taking on too many responsibilities. It's hard to know when to stop.

React lost me when it stopped being a rendering library and became a "runtime" instead. What do you know, when a runtime starts collapsing rendering, data fetching, caching, authorization boundaries, server and client into a single abstraction, the blast radius of any mistake becomes enormous.

hu32• 7 months ago

I never saw brilliance in his contributions. Specially as React keeps being duct-taped.

Making complex things complex is easy.

Vue on the other hand is just brilliant. No wonder it's creator, Evan You went on to also create Vite. A creation so superior that it couldn't be confined to Vue and React community adopted it.

https://evanyou.me

epolanski2• 7 months ago

There's no need to take down and diminish other's contributions, especially in open source where everybody's free to bring a better solution to the table.

Or just fork if the maintainers want to go their way. If your solution has its merits it will find its fans.

metta2uall• 7 months ago

For the vast majority of projects it seems like the disadvantages of these highly complex RPC systems far exceed the benefits... Not just in terms of security but also the reduced observability compared to simple JSON..

TZubiri7• 7 months ago

Interesting how DoS ranks higher than code exposure in severity.

I personally think it's the other way around, since code exposure increases the odds that a security breach happens, while DoS does not increase chances of exposure, but affects reliability.

Obviously we are simplifying a multidimensional severity to one dimension, but I personally think that breaches are more important than reliability. I'd rather have my app go down than be breached.

And I don't think it's a trivial difference, if you'd rather have a breach than downtime, you will have a breach.

LittleOtter• 7 months ago

Our team is working to fix our Next.js project.It's so painful.

Now I'm doubting RSC is a good engineering technology or a good practice.The real world is tradeoffs: RSC really help us improve our develop speed as we have good teamates that has good understanding of fullstack.

Do hope such things won't happen again.

IceDane2• 7 months ago

How is it painful? You need to bump a minor version? It took me less than 5 minutes 90% of which was waiting for CI. There's even a tool you can run to do it for you.

phplovesong• 7 months ago

SSR is just dumb. Its very rare that you would benefit much from this approach, the only thing you get an complexity bomb exploding in your face.

How about either just return html (maybe with htmx), or have a "now classic" SPA.

The frontend must be the most over engineered shitshow we as devs have ever created. Its where hype meets the metal.

nathants• 7 months ago

Just exchange json.

Backend in python/ruby/go/rust.

Frontend in javascript/typescript.

Scripts in bash/zsh/nushell.

One upon a time there was a low amount of friction and boilerplate with this approach, but with Claude and Codex it’s changed from low to none.

KronisLV• 7 months ago

I really like having a good old RESTful API (well maybe kinda faking the name because don't need HATEOAS usually)!

Except I find most front end stacks to lead to either endless configuration (e.g. Vue with Pinia, router, translation, Tailwind, maybe PrimeVue and a bunch of logic for handling sessions and redirects and toast messages and whatnot) and I feel the pull to just go and use Django or Laravel or Ruby on Rails mostly with server side templates - I much prefer that simplicity, even if it feels a bit icky to couple your front end and back end like that.

ManuelKiessling• 7 months ago

I really wonder why the swarm intelligence of software developers still hasn’t decided on a single best clearly defined architecture for serving web applications, decades after the building blocks have been in place.

Let the server render everything. Let JS render everything, server is only providing the initial div and serves only JSON from then on. Actually let JS render partial HTML rendered on the server! Websockets anyone?

Imagine SQL server architecture or iOS development had this kind of ADHS syndrome.

dzonga• 7 months ago

react server components is something that should've never existed anyway.

are people shipping faster due to them ? or it's all complexity, security vulnerabilities like this. you're not facebook. render html the classic way if you need server rendered html. if you really do need an SPA - which is 5% of the apps out there - then yeah use client side react, vue, svelte etc - none of those RPC server actions etc

CodingJeebus2• 7 months ago

Agreed. Unfortunately, there's an entire content/bootcamp ecosystem pushing this stuff that came of age largely during the tech boom, as well as a bunch of early and mid-career devs and companies that are deeply tied to it. With major VC funding backing projects like Bun, Vercel, etc., I don't think this deeply flawed approach to development is going anywhere because the utopian JS fantasy of "it just works and runs everywhere flawlessly" is the ultimate myth of building for the web.

scotty79• 7 months ago

Language with dynamic code evaluation on the server plus fat client-setver protocol that attempts to sync raw objects of the language. What could have gone wrong?

I wonder if similar magic fat pipe technologies (like Blazor) have similar vulnerabilities waiting to be discovered. Maybe compiled languaged are safer by default in this scenario, but anything built in Python, PHP, Ruby or any "code is data" language would probably fare similarly poorly.

Denial of service and source code exposure in React Server Components

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