Oracle Security: SQL Injection

What is SQL Injection ?

SQL injection is a technique to maliciously exploit applications that use client-supplied data in SQL statements. Attackers trick the SQL engine into executing unintended commands by supplying specially crafted string input, thereby gaining unauthorized access to a database in order to view or manipulate restricted data.

How does SQL Injection take place?

Incorrectly validated or nonvalidated string literals are concatenated into a dynamic SQL statement, and interpreted as code by the SQL engine. The code passage below is an example of code that is vulnarable for SQL Injection:

create or replace procedure show_col (p_colname varchar2, p_tablename varchar2) AS
type t is varray(200) of varchar2(25);
results t;
stmt CONSTANT VARCHAR2(4000) := 'select '||p_colname|| ' from scott.'||p_tablename;
BEGIN
   dbms_output.put_line('SQL Stmt: '||stmt);
   execute immediate stmt bulk collect into Results;
   for j in 1..Results.Count() loop
      dbms_output.put_line(results(j));
   end loop;
END show_col;
/

Let's first run it for it's intented use, as a harmless user:

set serveroutput on
SQL> execute show_col('ENAME','EMP');
SQL Stmt: select ENAME from scott.EMP
SMITH
ALLEN
WARD
JONES
MARTIN
BLAKE
CLARK
SCOTT
KING
TURNER
ADAMS
JAMES
FORD
MILLER

PL/SQL procedure successfully completed.