fixes a protocol weakness in the golang.org/x/crypto/ssh package that allowed a MITM attacker to compromise the integrity of the secure channel before it was established, allowing them to prevent transmission of a number of messages immediately after the secure channel was established without either side being aware. The impact of this attack is relatively limited, as it does not compromise confidentiality of the channel. Notably this attack would allow an attacker to prevent the transmission of the SSH2 MSG EXT INFO message, disabling a handful of newer security features.