CVE-2022-39255 Information

Description

Matrix iOS SDK allows developers to build iOS apps compatible with Matrix. Prior to version 0.23.19 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. matrix-ios-sdk version 0.23.19 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. To avoid malicious backup attacks one should not verify one’s new logins using emoji/QR verifications methods until patched.

Reference

https://matrix.org/blog/2022/09/28/upgrade-now-to-address-encryption-vulns-in-matrix-sdks-and-clients https://github.com/matrix-org/matrix-ios-sdk/security/advisories/GHSA-hw6g-j8v6-9hcm https://github.com/matrix-org/matrix-ios-sdk/releases/tag/v0.23.19 https://github.com/matrix-org/matrix-ios-sdk/commit/5ca86c328a5faaab429c240551cb9ca8f0f6262c