CVE-2022-39251

Matrix Javascript SDK is the Matrix Client-Server SDK for JavaScript. Prior
to version 19.7.0, an attacker cooperating with a malicious homeserver can
construct messages that legitimately appear to have come from another
person, without any indication such as a grey shield. Additionally, a
sophisticated attacker cooperating with a malicious homeserver could employ
this vulnerability to perform a targeted attack in order to send fake
to-device messages appearing to originate from another user. This can
allow, for example, to inject the key backup secret during a
self-verification, to make a targeted device start using a malicious key
backup spoofed by the homeserver. These attacks are possible due to a
protocol confusion vulnerability that accepts to-device messages encrypted
with Megolm instead of Olm. Starting with version 19.7.0, matrix-js-sdk has
been modified to only accept Olm-encrypted to-device messages. Out of
caution, several other checks have been audited or added. This attack
requires coordination between a malicious home server and an attacker, so
those who trust their home servers do not need a workaround.