One of the purposes of the JDK patch is to prevent '\ r' and '\ n' from being inserted into the ftp command. In particular, it seems to assume that if another malice command is inserted after '\ n', the possibility of such an attack will be opened at a later time.
IMO, I think that we can block '\ r \ n' and '\ n' at the same time by blocking only '\ n'. Although '\ r' allows