Hello, I have a problem with CORS and I think this is right community to get help.
When I use this code:
import { LemmyHttp } from 'lemmy-js-client';
const client = new LemmyHttp('https://lemmy.ml');
const { posts } = await client.getPosts({
limit: 10,
page: 1
});
to get posts from lemmy.ml (using lemmy-js-client), I get:
Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://lemmy.ml/api/v3/post/list?limit=10&page=1. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing). Status code: 400.
I have tried to add header like this:
const client = new LemmyHttp('https://lemmy.ml', {
headers: {
'Access-Control-Allow-Origin': '*'
}
});
but result is the same.
Can someone help me with this?
curl doesn’t care about CORS, CORS is a browser implementation.
For CORS to work the url should be returning a header of
access-control-allow-origin : *
(or an header specific to the origin)It seems like they are working on it: https://github.com/LemmyNet/lemmy/pull/3421
So I’ll have to wait for this PR to be merged. I think they will do it soon because it provides more positive value that negative at this moment
I don’t know if the PR is going to solve it though.
If I’m looking at the file changed: https://github.com/LemmyNet/lemmy/pull/3421/files
It seems like the “Lemmy Instance Owner” would have to set an environment variable of “
LEMMY_CORS_ORIGIN
” - and if there’s no variable set it defaults back to:I don’t know if instances are going to “allow *”
I haven’t found
.allow_any_origin()
in source (query), but isn’t it sorta equivalent toAccess-Control-Allow-Origin: *
? Or I’m misinterpreting somethingEdit: from the author of PR:
Setting it to
*
will prevent the browser from including credentials in the request (cookies). Dynamically setting it to the origin of the requesting client effectively does the same but also allows for using credentials.I don’t think it would be a very good implementation to just let any site dynamically request to be allowed by CORS, including with credentials… A malicious site could do way too many things on the users behave
A possible solution would be something like how reddit or github do it - have the user first accept an “Allow third party app / website to access my account” - and after that, add those sites to the
Access-Control-Allow-Origin
What are the exact attack vectors you’re thinking of?
Well I’m not expert on CORS, nor with the Lemmy API, so it’s probably better to read about CORS exploits in more detailed articles… https://www.freecodecamp.org/news/exploiting-cors-guide-to-pentesting/ for example
It seems Lemmy is storing a JWT in the cookiejar, so with
Access-Control-Allow-Credentials:true
and the domain inAccess-Control-Allow-Origin
a site should be able to do authenticated get requests on a users behave with the JWT, and access personal data.The “GET https://programming.dev/api/v3/private_message/” endpoint for example, would let someone read the private messages someone has send/received
I’m not sure whether someone could do POST requests and add credentials from the cookiejar this way though
yes but OP still can’t do anything on the client side, it should be configured on the server