Ok, boolean tribe..the hoores feel very much protected still by Oracle. So, let me be a bitch and not an intelectual! Let'me digg this 1st aspect " the actual username can be spoofed by use of BECOME USER. This leads to the fact that some spoofing can be done before the session" I want to transfer data from the piece of shit, not exacly on a MIM's. So I do get in, as BECOME USER?let me start beeing a bitch! over with brains olympic games NSA!

How to become another User in SQLPlus

See this link for a much better way to achieve this in current releases, using proxy users...
A DBA frequently needs to become another user to test something or verify a problem.  Short of having to gain acess to that users password, we are asked can I su to that account, sort of like root does on unix.
This is an 'su.sql' script I use:
 

whenever sqlerror exitcolumn password new_value pw
declare
    l_passwd varchar2(45);
begin
    select password into l_passwd
      from sys.dba_users
     where username = upper('&1');
end;
/
select password
  from sys.dba_users
 where username = upper( '&1' )
/
alter user &1 identified by Hello;
connect &1/hello
alter user &1 identified by values '&pw';
show user
whenever sqlerror continue

it starts by testing your access to the sys.dba_users table -- if that fails -- it exits SQLPlus.  If zero rows returned -- it exits SQLPlus.
It then selects the 'password' from the dba_users table and stuffs it into a macro variable "&pw"
We alter the user you want to become to have a known password (if that fails, we exit).
We 'fix' their password back after loggin in as them....
Note, you need to have access to dba_users and the alter user privelege.

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https://asktom.oracle.com/Misc/su.html