BJT configurations input
The base node is - obviously - ONE single node only. 

However, a voltage is defined as the difference in potential BETWEEN TWO nodes.
As a consequence - and according to the working principle of the BJT - the voltage between the base node and the emitter is the input for ALL three configurations.

However, one of these nodes is grounded (ac wise) and , thus, defines the three basic configurations.   

EDIT (Comment):  (Regarding the comment from Spehro Pefhany)

Also in common-base configuration, it is the base-emitter voltage that controls the collector current Ic.That means: When the base is grounded, it is the emitter voltage referenced to ground.

(After changing the PC machine a new account was automatically created and I am not yet allowed to write a "comment".)