Sunday, 11 November 2012

How to prevent mysql sleep injections?

Recently, we faced an issue with website which was developed around one year back. One hacker successfully tried to slow the website using sleep injection. Although we were using precautions like mysqli_real_escape_string() for escaping SQL string syntax correctly. Let’s see why this happened then and what are the solutions?

We were using following code to get product id passed through query string.

$id   = mysqli_real_escape_string($con , (isset($_REQUEST['id']) ? $_REQUEST['id'] : 0));
$qry = "Select * from products where id = ".$id;

but hacker tried to change the the query string as : 

?id=3 and sleep(4)

and query becomes

Select * from products where id = 3 and sleep(4);

And it started taking around 4+seconds to run the query. So in this way website become too slow.

We were trying to figure out the possible and the best solution.

After spending some time we noticed that although we were using mysqli_real_escape_string() function but we were not using it properly. Everytime we use mysqli_real_escap_string(), the returned string must be used with single quotes although it’s numeric or string. So quick solution for that problem was to change the query as :

$id   = mysqli_real_escape_string($con , (isset($_REQUEST['id']) ? $_REQUEST['id'] : 0));
$qry = "Select * from products where id = ‘".$id."";

It is a quick solution but not the best one.

We could have also checked if the input is numeric or not.

Note : For future reference I would like to say please don’t use mysql_ extensions anymore. mysql_ extension is deprecated as of PHP 5.5, and will be removed in future.

Use mysqli or PDO prepared statements. Best is PDO statements.

The internet (and many respectable CS courses) are littered with examples using mysql_query() and string concatenation, half of which train people to create SQLI bugs or don't explain why escaping is needed; it's too late to undo the damage already done but at least people new to PHP will hopefully be told now that there is a better way. Although we can’t say PDO is 100% not vulnerable to errors but we don’t need to use external functions to cover sql injections. So as a programmer I would suggest and request to all the developers community to use PDOs in future reference.

Reference :

Thanks!!!!!!!!!!!!!! Enjoy Programming :)

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