Headline
CVE-2023-29529: Invisible eavesdropping in group calls
matrix-js-sdk is the Matrix Client-Server SDK for JavaScript and TypeScript. An attacker present in a room where an MSC3401 group call is taking place can eavesdrop on the video and audio of participants using matrix-js-sdk, without their knowledge. To affected matrix-js-sdk users, the attacker will not appear to be participating in the call. This attack is possible because matrix-js-sdk’s group call implementation accepts incoming direct calls from other users, even if they have not yet declared intent to participate in the group call, as a means of resolving a race condition in call setup. Affected versions do not restrict access to the user’s outbound media in this case. Legacy 1:1 calls are unaffected. This is fixed in matrix-js-sdk 24.1.0. As a workaround, users may hold group calls in private rooms where only the exact users who are expected to participate in the call are present.
Impact
An attacker present in a room where an MSC3401 group call is taking place can eavesdrop on the video and audio of participants using matrix-js-sdk, without their knowledge. To affected matrix-js-sdk users, the attacker will not appear to be participating in the call.
This attack is possible because matrix-js-sdk’s group call implementation accepts incoming direct calls from other users, even if they have not yet declared intent to participate in the group call, as a means of resolving a race condition in call setup. Affected versions do not restrict access to the user’s outbound media in this case.
Legacy 1:1 calls are unaffected.
Patches
This is fixed in matrix-js-sdk 24.1.0.
Workarounds
Users may hold group calls in private rooms where only the exact users who are expected to participate in the call are present.
References
None applicable.
For more information
If you have any questions or comments about this advisory please email us at security at matrix.org.
Related news
### Impact An attacker present in a room where an [MSC3401](https://github.com/matrix-org/matrix-spec-proposals/pull/3401) group call is taking place can eavesdrop on the video and audio of participants using matrix-js-sdk, without their knowledge. To affected matrix-js-sdk users, the attacker will not appear to be participating in the call. This attack is possible because matrix-js-sdk's group call implementation accepts incoming direct calls from other users, even if they have not yet declared intent to participate in the group call, as a means of resolving a race condition in call setup. Affected versions do not restrict access to the user's outbound media in this case. Legacy 1:1 calls are unaffected. ### Patches This is fixed in matrix-js-sdk 24.1.0. ### Workarounds Users may hold group calls in private rooms where only the exact users who are expected to participate in the call are present.