Mysqli query Injection , how to inject the SQL query string? - php

Question

Let's consider i have this line of code
$result = $mysqli->query("SELECT * from myTable where field='".$_GET['var']."');
IMHO this is vulnerable to SQL injections.
So I'd like to prove it trying by sending via Get / URL a "var" param that will inject the query, with potential malicious code.
I actually tryed this:
var = "1'; TRUNCATE myTable; ";
I tryed to print out the SQL string query before executing it and it's actually 2 SQL valid statements.
SELECT * from myTable where field='1'; TRUNCATE myTable;
1st problem
But actually itseems that mysqli->query will not execute 2 statements at once. Isn't it?
2nd problem
I see that a common technique to Inject queries is to per form injection then add comment chars to get rid of the tail of the SQL.
Example:
"SELECT * from myTable where field='".$_GET['var']."' AND field2 IS NOT NULL"
Can be injected with :
var = "1'; TRUNCATE myTable; # ";
But this problem arise and I'm missing the trick to get rid of it
if the SQL string in the code have new lines e.g. :
"SELECT * from myTable where field='".$_GET['var']."'
AND field2 IS NOT NULL"
If i use the above "var" the final result is
SELECT * from myTable where field='1'; TRUNCATE myTable; #
AND field2 IS NOT NULL
Second line won't be commented
How to test injection on this?
Many thanks.

Answer 1

1st problem But actually it seems that mysqli->query will not execute 2
statements at once. Isn't it?
That's right, if you want to execute multiple statements you need to use mysqli->multi_query. You can find a good explanation about multiple statements here: http://www.php.net/manual/en/mysqli.quickstart.multiple-statement.php
But this problem arise and I'm missing the trick to get rid of it
The problem arises because you are using multiple statements, and mysqli->query does not support them.
About your queries:
$result = $mysqli->query("SELECT * from myTable where field='".$_GET['var']."');
You can inject this using for example 1' OR 1=1; that would return all entries of myTable on the query result.
"SELECT * from myTable where field='".$_GET['var']."' AND field2 IS NOT NULL"
Here you could use 1' OR 1=1 UNION ALL SELECT * FROM myTable WHERE '1'='1
Nowadays there are tools that can automatically check SQL injection for you, take a look at SQL Inject Me (Firefox Addon) for example.