Impact The message edit validation logic in the "matrix-sdk-ui" crate before 0.16.1 is missing a check: when replacing an encrypted event, the replacement event itself is not required to be encrypted. This enables a malicious homeserver administrator (or an actor with equivalent power) to impersonate or spoof messages as if they were sent by a victim user. Patches "matrix-sdk-ui" 0.16.1 fixes the message edit validation logic to align with the algorithm for replacement events"^1" (https://spec.matrix.org/unstable/client-server-api/#validity-of-replacement-events) described in the Matrix specification. Workarounds N/A References * Pull request: https://github.com/matrix-org/matrix-rust-sdk/pull/6454 For more information If you have any questions or comments about this advisory, please email us at "security at matrix.org" (mailto:security@matrix.org).