CODEWITHSUNDEEP
sqlplsqlcode-injection
Gico
Gico

Reputation: 1394

SQL Injection in PL/SQL - myth or fact?

I am trying to hack my PL/SQL code. We create the PL/SQL procedure that opens and fetch the cursor. By our standard we did create a dynamic SQL statement, but we are unable to inject the OR 1=1 condition.

I did prepare a http://sqlfiddle.com/#!4/a62a3/5 demo, where you can try to inject the code. 

CREATE FUNCTION get_documents (p_document_id IN DOCUMENTS.DOCUMENT_ID%TYPE)
    RETURN SYS_REFCURSOR
AS
    p_rs SYS_REFCURSOR;
BEGIN
    DBMS_OUTPUT.PUT_LINE('------ INPUT VALUES ------');
    DBMS_OUTPUT.PUT_LINE('p_document_id: ' || p_document_id);

    OPEN p_rs FOR 
        SELECT DOCUMENT_ID, '(' || MY_FIELD || ')' FROM DOCUMENTS WHERE DOCUMENT_ID = '' ||  p_document_id  || '';
    RETURN p_rs;
END;

We tried to inject the code in p_document_id parameter. We set it to: 

 document_refcur_local:=get_documents('10'' OR 1=1; -- ');

but we were unable to select all records. Could you please let me know what am I doing it wrong?

Upvotes: 5

Views: 2875

Answers (3)

Aleksej
Aleksej

Reputation: 22949

An example:

create table documents (id, value) as 
(
    select 1, 'x' from dual union all
    select 2, 'x' from dual union all
    select 3, 'y' from dual
)

A vulnerable function:

create or replace function countDocs(pValue IN varchar2) return number is
    vRetVal number;
begin
    execute immediate 'select count(*) from documents where value = ''' || pValue || ''''
    into vRetVal;
    return vRetVal;
end;

What you can do:

SQL> select countDocs('y') from dual;

COUNTDOCS('Y')
--------------
             1

SQL> select countDocs('y'' or ''a''=''a') from dual;

COUNTDOCS('Y''OR''A''=''A')
---------------------------
                          3

A safe way could be with bind variables:

create or replace function countDocsSafe(pValue IN varchar2) return number is
    vRetVal number;
begin
    execute immediate 'select count(*) from documents where value = :bindVar'
    into vRetVal
    using pValue ;
    return vRetVal;
end;

Which gives:

SQL> select countDocsSafe('y') from dual;

COUNTDOCSSAFE('Y')
------------------
                 1

SQL> select countDocsSafe('y'' or ''a''=''a') from dual;

COUNTDOCSSAFE('Y''OR''A''=''A')
-------------------------------
                              0

Upvotes: 2

Bob Jarvis - Слава Україні
Bob Jarvis - Слава Україні

Reputation: 50017

If you want to succeed at SQL injection your SELECT statement needs to be specified as a character string to which you concatenate your document ID string, which contains the condition to be added. Here's your code, rewritten:

CREATE OR REPLACE FUNCTION GET_DOCUMENTS (p_document_id IN VARCHAR2)
  RETURN SYS_REFCURSOR
IS
  p_rs SYS_REFCURSOR;
BEGIN
  DBMS_OUTPUT.PUT_LINE('------ INPUT VALUES ------');
  DBMS_OUTPUT.PUT_LINE('p_document_id: ' || p_document_id);

  OPEN p_rs FOR 
    'SELECT DOCUMENT_ID, ''('' || MY_FIELD || '')'' FROM DOCUMENTS WHERE DOCUMENT_ID = ''' ||  p_document_id  || '''';

  RETURN p_rs;
END GET_DOCUMENTS;

Upvotes: 4

Milney
Milney

Reputation: 6417

This is not in fact a dynamic statement and so is not vulnerable to an injection.

If you built this string from a front-end with string concatenation of the p_document_id outside of the SQL query - then sent it to SQL, it would be vulnerable, but you cannot do the injection in the SQL query itself (Unless building a string then running it, i.e. a dynamic query, which yours is not doing)

A dynamic query vulnerable to injection would look more like;

EXECUTE IMMEDIATE 'SELECT * FROM DOCUMENTS WHERE DOCUMENT_ID = ''' + someUserInput + ''''

And you could inject by passing as someUserInput something like

' OR 1=1; --

Upvotes: 5

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