The ability to execute arbitrary SQL on Oracle via a SQL injection flaw is hampered by the fact that the Oracle RDBMS will not batch multiple queries. Typically, a low privileged attacker with say only the CREATE SESSION privilege, must find a function they can inject that will allow them to execute a block of anonymous PL/SQL. These are known as auxiliary inject functions. Depending upon the version of Oracle and what components are installed auxiliary inject functions may be few and far between. For example, on Oracle 12c with the internal Java VM removed, there may be none. Indeed, during a recent client assessment the author of this paper was confronted with such a situation: a PL/SQL injection flaw but with no easy method for easy exploitation to gain full control of the database server. This paper presents a method around such a problem using DBMS_XMLSTORE and, co-incidentally, DBMS_XMLSAVE. This method can be used in web-based SQL injection attacks, as well.
You can download it from the following link: https://packetstormsecurity.com/files/download/127552/DBMS_XMLSTORE_PLSQL_Injection.pdf
Source: https://packetstormsecurity.com/files/127552/DBMS_XMLSTORE-As-An-Auxiliary-SQL-Injection-Function-In-Oracle-12c.html