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.