matrix-sdk-crypto vulnerable to sender of encrypted events being spoofed by homeserver administrator
Date: 2025-06
Affected: rust/matrix-sdk-crypto
Attack vector: other
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2025-48937
CWE: CWE-290
CVSS: 4.9 (CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N)

### Summary matrix-sdk-crypto since version 0.8.0 up to 0.11.0 does not correctly validate the sender of an encrypted event. Accordingly, a malicious homeserver operator can modify events served to clients, making those events appear to the recipient as if they were sent by another user. Although the CVSS score is 4.9 (AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N), we consider this a High Severity security issue. ### Details The Matrix specification [requires](https://spec.matrix.org/v1.14/client-server-api/#mmegolmv1aes-sha2) that clients ensure that "the event’s `sender`, `room_id`, and the recorded `session_id` match a trusted session". The vulnerable matrix-sdk-crypto versions check that the `room_id` matches that of the session denoted by `session_id`, but do not check the `sender`. ### Patches The issue is resolved by [13c1d20](https://github.com/matrix-org/matrix-rust-sdk/commit/13c1d2048286bbabf5e7bc6b015aafee98f04d55), included in versions 0.11.1 and 0.12.0 of matrix-sdk-crypto. ### Workarounds Since a successful attack requires administrator access to the homeserver, users who trust the administrators of their local homeserver are not affected. ### References * https://spec.matrix.org/v1.14/client-server-api/#mmegolmv1aes-sha2


Mitigations:

Architectural layers (MAESTRO):