Can't join (federated) channels due to missing CORS header on app.element.io (affects Web & Mobile)

[Nexus2k]

Steps to reproduce

1. Where are you starting? What can you see?

• I've got an invitation to join a room/DM from a self-hosted matrix instance

3. What do you click?

• I try to click "Start chatting" but receive a 502 error CORS error messages in the Developer Console

On Mobile (Android 14) I do receive an HTTP error 502 during the same action/attempt to join.

Outcome

What did you expect?

Able to join the chat room

What happened instead?

I receive an error about a missing CORS header:

Access to fetch at 'https://matrix-client.matrix.org/_matrix/client/v3/join/XXXXXXXX' from origin 'https://app.element.io' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

Operating system

Windows

Browser information

Chrome 128.0.6613.120 (Offizieller Build) (64-Bit)

URL for webapp

https://app.element.io/

Application version

Element version: 1.11.76 Crypto version: Rust SDK 0.7.1 (c8c9d15), Vodozemac 0.6.0

Homeserver

matrix.org

Will you send logs?

Yes

[Nexus2k]

This problem is no longer reproducible. Not sure if something was fixed on element.io side.

[t3chguy]

Not sure if something was fixed on element.io side.

It would have been a matrix.org issue, given it is the server which is responsible for sending the CORS headers as per the Matrix spec: https://spec.matrix.org/v1.11/client-server-api/#web-browser-clients