Protect against SQL injection

Question

I'm developing a website and I'm trying to secure the connection part.

I used the addslashes function on $login to stop SQL injection but some friends told me that's not enough security. However, they didn't show me how to exploit this vulnerability.

How can I / could you break this code? How can I secure it?

<?php

    if ( isset($_POST) && (!empty($_POST['login'])) && (!empty($_POST['password'])) )
    {
        extract($_POST);
        $sql = "SELECT pseudo, sex, city, pwd FROM auth WHERE pseudo = '".addslashes($login)."'";
        $req = mysql_query($sql) or die('Erreur SQL');
        if (mysql_num_rows($req) > 0)
        {
            $data = mysql_fetch_assoc($req);
            if ($password == $data['pwd'])
            {
                $loginOK = true;
            }
        }
    }
    ?>

Answer 1

You should use mysql_real_escape_string for escaping string input parameters in a query. Use type casting to sanitize numeric parameters and whitelisting to sanitize identifiers.

In the referenced PHP page, there is an example of a sql injection in a login form.

A better solution would be to use prepared statements, you can do this by using PDO or mysqli.