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

Rather than addslashes you should use mysql_real_escape_string.

Answer 2

Use:

mysql_real_escape_string($inputToClean);

Answer 3

There's another gaping security hole - extract. It may save you from typing a few characters, but opens up holes too numerous to mention, for it will overwrite any global variables.

What happens if I post this?

$_POST {
    'login' => 'Admin',
    'loginOK' => 1
}

Guess what, $loginOK is now == 1 , and I'll be logged in as Admin.

Save yourself a lot of grief later, and just use the variables you want to use, instead of relying on the horrible hack that is extract.

Answer 4

Apart from the usage of addslashes(), these are some random issues found in this code:

• isset($_POST) is always TRUE, unless you run it from the command line. You can probably remove it.
• empty() is very tricky. For instance, if $password = '0' then empty($password) is TRUE.
• You can do this: if( isset($_POST['login']) && $_POST['login']!='' ){}
• extract($_POST) is a huge vulnerability: anyone can set variables in your code from outside.
• $password == $data['pwd'] suggests that you are storing plain text passwords in your database. That's a terrible practice. Google for "salted password".
• You can also do $loginOK = $password == $data['pwd'];. Do you realise why? ;-)

Answer 5

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.

Answer 6

You are storing your passwords in plaintext! That's a major security issue if ever I saw one. What to do about that: at least use a (per-user) salted hash of the password, as seen e.g. here.