CVE-2022-39251

Name of the Vulnerable Software and Affected Versions Matrix Javascript SDK versions prior to 19.7.0

Description The issue allows an attacker cooperating with a malicious homeserver to construct messages that appear to come from another person without indication. A sophisticated attacker could employ this vulnerability to perform a targeted attack, sending fake to-device messages appearing to originate from another user. This can allow injecting the key backup secret during self-verification, making a targeted device use 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. The attack requires coordination between a malicious homeserver and an attacker.

Recommendations For versions prior to 19.7.0, update to version 19.7.0 or later, which only accepts Olm-encrypted to-device messages and includes additional checks for security. As a precaution, avoid using emoji/QR verification methods for new logins until patched, and instead, verify with your security passphrase. If you trust your homeserver, no particular workaround is needed.