SQL & PL/SQL

Hi, how do i extract multiple values from a string with RegExp constructs with Oracle SQL?

I have looked at the various examples but can not figure this out .
the following Sql

select
   regexp_substr(sessie."rollen", 'CN=A_role') "A_role"
   from ( 
select '
CN=A_role,OU=a_org_unit,OU=another_org_unit,DC=bz,DC=ad,DC=min,DC=local
CN=Another_role,OU=some_org_unit,DC=bz,DC=ad,DC=min,DC=local
CN=Users,OU=Dep,DC=bz,DC=ad,DC=min,DC=local
'   "rollen" from dual
) sessie;

just returns CN=A_role.
I want it to return all of the CN= values concatenated with a semicolon and stripped from the CN= bit.
So: A_role;Another_role;Users .

Any help would be deeply appreciated. I am using 11g 11.2.0.2.0 database here.

Does anybody have any idea how to do this in SQL ?

kind regards Mike