Mellium mellium.im/xmpp 0.0.1 through 0.21.4 allows response spoofing if the implementation uses predictable IDs because the stanza type is not checked. This is fixed in 0.22.0.

In Mellium mellium.im/xmpp through 0.21.0, an attacker capable of spoofing DNS TXT records can redirect a WebSocket connection request to a server under their control without causing TLS certificate verification to fail. This occurs because the wrong host name is selected during this verification.