CVE-2022-39254

matrix-nio is a Python Matrix client library, designed according to sans I/O principles. Prior to version 0.20, when a users requests a room key from their devices, the software correctly remember the request. Once they receive a forwarded room key, they accept it without checking who the room key came from. This allows homeservers to try to insert room keys of questionable validity, potentially mounting an impersonation attack. Version 0.20 fixes the issue.

matrix-nio is a Python Matrix client library, designed according to sans I/O principles. Prior to version 0.20, when a users requests a room key from their devices, the software correctly remember the request. Once they receive a forwarded room key, they accept it without checking who the room key came from. This allows homeservers to try to insert room keys of questionable validity, potentially mounting an impersonation attack. Version 0.20 fixes the issue.

When matrix-nio before 0.20 requests a room key from our devices, it correctly accepts key forwards only if they are a response to a previous request. However, it doesn't check that the device that responded matches the device the key was requested from. This allows a malicious homeserver to insert room keys of questionable validity into the key store in some situations, potentially assisting in an impersonation attack. ### For more information If you have any questions or comments about this advisory, e-mail us at [poljar@termina.org.uk](mailto:poljar@termina.org.uk).

When matrix-nio before 0.20 requests a room key from our devices, it correctly accepts key forwards only if they are a response to a previous request. However, it doesn't check that the device that responded matches the device the key was requested from. This allows a malicious homeserver to insert room keys of questionable validity into the key store in some situations, potentially assisting in an impersonation attack. ### For more information If you have any questions or comments about this advisory, e-mail us at [poljar@termina.org.uk](mailto:poljar@termina.org.uk).

matrix-nio es una librería cliente de Matrix en Python, diseñada según los principios de sans I/O. En versiones anteriores a 0.20, cuando los usuarios solicitaban una llave de habitación desde sus dispositivos, el software recordaba correctamente la petición. Una vez que reciben una llave de habitación reenviada, la aceptan sin comprobar de quién procede la llave de habitación. Esto permite que los servidores domésticos intenten introducir llaves de habitación de dudosa validez, montando potencialmente un ataque de suplantación de identidad. La versión 0.20 corrige el problema