Attacking unuauthenticated RSA In symmetric cryptography, a scheme is not considered secure if the data transmitted is only encrypted. The adversary will be able to modify messages to generate encrypted messages of his choice without having the key.

Is this applicable to asymmetric crypto such as RSA?
The attack is even more simple with RSA than with symmetric keys, because the asymmetric encryption key is assumed to be public.

Let me tell you a story involving Alice, Bob and Mallory :). Alice wants to send a message to Bob using RSA. 


Alice encrypts the message using Bob's public key and sends it
Mallory performs a Man-In-The-Middle attack, and encrypts another message using Bob's public key (as it's public)
Bob received the new message thinking it comes from Alice, as there's no origin authentication.