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.

mellium.im/sasl: insufficient randomness during authentication

An issue was discovered in Mellium mellium.im/sasl before 0.3.1. When performing SCRAM-based SASL authentication, if the remote end advertises support for channel binding, no random nonce is generated (instead, the nonce is empty). This causes authentication to fail in the best case, but (if paired with a remote end that does not validate the length of the nonce) could lead to insufficient randomness being used during authentication.

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.