matrix-react-sdk is a react-based SDK for inserting a Matrix chat/voip client into a web page. A malicious homeserver could manipulate a user's account data to cause the client to enable URL previews in end-to-end encrypted rooms, in which case any URLs in encrypted messages would be sent to the server. This was patched in matrix-react-sdk 3.105.0. Deployments that trust their homeservers, as well as closed federations of trusted servers, are not affected. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Matrix SDK for React's URL preview setting for a room is controllable by the homeserver