Matrix Rust SDK: Sender-binding gaps in to-device and room-key attribution

Impact

The matrix-sdk-crypto crate before 0.16.1 is missing a check for the sender's user ID when decrypting an Olm-encrypted to-device message containing the sender_device_keys property.

This could be exploited to spoof the sender of an encrypted to-device message, but only if the attacker colludes with (or is) the homeserver operator.

Patches

This issue is fixed in matrix-sdk-crypto 0.16.1.

Workarounds

There are no known workarounds for the issue.

References

This issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/6553.

For more information

If you have any questions or comments about this advisory, please email us at security at matrix.org.