41–50 of 285 posts
I'm one of them. CORS is THE topic that I have to get a refresher for periodically. It's like I forget about it, it never sticks. I'm a backend developer so I never encounter any cors issues. Maybe that's why? I seem to forget things that I don't use on a day to day basis, so.
I agree that CORS is hard to understand and fix. I was the CTO at an auth company and SO many of our users used to run into various CORS issues and asked questions on our support. However, I'd now argue that developers don't need to understand CORS anymore.. cause claude / gpt does! Just throw in the error in claude code / codex and it would fix it.
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I agree that CORS is hard to understand and fix. I was the CTO at an auth company and SO many of our users used to run into various CORS issues and asked questions on our support. However, I'd now argue that developers don't need to understand CORS anymore.. cause claude / gpt does! Just throw in the error in claude code / codex and it would fix it.
"So let me get this straight. We tell the client whether the application we gave them can or cannot make requests to our servers. And none of this actually prevents the client from making the requests if they want to?... Pull the other one it has bells on."
It took a good sleep and a long shower to under stand it. "Oh... it is for if I want to do a self injection attack and allow random untrusted malicious code in my application. In other words, ads"
Basically the threat model is inverted from any other threat model, that is why it looks so stupid. CORS is threat model used for when you can't trust your self.
It's not just CORS that's hard to understand. Many (most?) developers don't really understand the threat model. And even when it's explained it hard to see why it's a big deal. Part of this is that backend developers usually have to configure CORS and it's not an access privilege protection. From the point of view of the backend it doesn't seem to matter. Bad guys can't get it. From the point of view of the front-end…
Earlier quoted context omitted.
> in the cors threat model an attacker gets one your users to take an action on your site by visiting their site This is really oversimplifying things, incorrectly IMO, and that sentence makes it sound like you're confusing a CSRF vulnerability with CORS protections. Normally when you write a backend server you implement some sort of authentication and access control, and in that scenario the threat model that lets "…
All CORS does is allow for selective loosening of anti-CSRF controls. CORS is a mechanism for a service to tell a client “I’m CSRF-resistant” so that that the client doesn’t need to protect its user as tightly when interacting with that service.
CORS _additionally_ requires OPTIONS pre-flight to succeed, before allowing any kind of request outside of what can be achieved with a HTML form submit action. So it blocks PUT/PATCH/DELETE, specifying most Content-Type, and specifying nearly all other headers. But this is just blocking "non-standard complex requests that might confuse badly programmed pre-javascript-era servers".
It passes all standard requests that you could have made by: embedding the url as an image src, the target of a HTML form, endpoint for csp reports, etc. All still need to be checked methodically by the server for CSRF if it's going to take any mutating action due to the request.
I agree that CORS is hard to understand and fix. I was the CTO at an auth company and SO many of our users used to run into various CORS issues and asked questions on our support. However, I'd now argue that developers don't need to understand CORS anymore.. cause claude / gpt does! Just throw in the error in claude code / codex and it would fix it.
It's me, CORS was the stupidest thing I encountered in a long line of stupid when trying to put together a simple web app for the first time. "So let me get this straight. We tell the client whether the application we gave them can or cannot make requests to our servers. And none of this actually prevents the client from making the requests if they want to?... Pull the other one it has bells on." It took a good sleep…
It's me, CORS was the stupidest thing I encountered in a long line of stupid when trying to put together a simple web app for the first time. "So let me get this straight. We tell the client whether the application we gave them can or cannot make requests to our servers. And none of this actually prevents the client from making the requests if they want to?... Pull the other one it has bells on." It took a good sleep…