How to protect himself ?

Do not use degraded modes

always know the key of its interlocutor as a preliminary

systematically check the key of the other party

immediately stop the connection in the event of anomaly

Caution:

numerous recommendations aren't serious !!!

except for slashdot readers, a quotation of Dug Song:

argh! it's amazing how silly some people are. Slashdot readers are especially numb-skulled, if their insistence that SSH2 would prevent such attacks is any indication.
i'll add compression support when i get a free second.