I got an email from Vercel urging to upgrade Next.js based project 3 days ago. POC was published 2 days ago. Today I’ve checked my logs and I could already see attack attempts.
We were very lucky that our usage was on the literal version before the affected version. Dodged a bullet.
This only affects sites that use the fancy new-fangled SSR rendering from what I’ve read. ReactJS (Client side) sites wouldn’t be affected.
Are we still vulnerable if our app doesn’t use React Server Functions endpoints?
Potentially. According to the React Team, even if React Server Functions are not in-use, the vulnerability is still exploitable if React Server Components are supported.
I think their point was that CSR-only sites would be unaffected, which should be true. Exploiting it on a static site, for example, couldn’t be RCE because the untrusted code is only being executed on the client side (and therefore is not remote).
Now, most people use, or at least are recommended to use, SSR/RSC these days. Many frameworks make SSR enabled by default. But using raw React with no Next.js, react-router, etc. to create a client-side only site does likely protect you from this vulnerability.
Now, most people use, or at least are recommended to use, SSR/RSC these days.
Why though?
I’m not the one recommending it lol.
If I had to guess, it’s to improve page performance by prerendering as much as possible, but I find it overkill and prefer to just prerender as much of the page as I can at build time and do CSR for the rest, though this doesn’t work if you have dynamic routes or some kind of server-side logic (good for blogs and such though).
I typically use React with only CSR, since I’m normally building apps with it over more static websites. Frameworks with SSR are popular, but there’s nothing wrong with an app that downloads and caches itself with a Service Worker when said app has a lot of interactivity and is likely to be used more than once.
Yeah been scrambling to get this one patched.
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