Matrix-React-SDK is a react-based SDK for inserting a Matrix chat/voip client into a web page. Before version 3.21.0, when uploading a file, the local file preview can lead to execution of scripts embedded in the uploaded file. This can only occur after several user interactions to open the preview in a separate tab. This only impacts the local user while in the process of uploading. It cannot be exploited remotely or by other users. This vulnerability is patched in version 3.21.0.

Impact 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.

Even if the CVSS score would be 4.1 (AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:N/A:N) the maintainer classifies this as High severity issue.

Patches This was patched in matrix-react-sdk 3.105.1.

Workarounds Deployments that trust their homeservers, as well as closed federations of trusted servers, are not affected.

References N/A.

matrix-react-sdk is an npm package which is a Matrix SDK for React Javascript. In matrix-react-sdk before version 3.15.0, the user content sandbox can be abused to trick users into opening unexpected documents. The content is opened with a blob origin that cannot access Matrix user data, so messages and secrets are not at risk. This has been fixed in version 3.15.0.