How to hack a website through (sql)

I want to worry you.



I want to show you just one way that hackers can get in to your website and mess

it up, using a technique called SQL Injection. And then I'll show you how to fix

it. This article touches on some technical topics, but I'll try to keep things

as simple as possible. There are a few very short code examples written in PHP

and SQL. These are for the techies, but you don't have to fully understand the

examples to be able to follow what is going on. Please also note that the

examples used are extremely simple, and Real Hackers will use many variations

on the examples listed.



If your website doesn't use a database, you can relax a bit; this article

doesn't apply to your site — although you might find it interesting anyway. If

your site does use a database, and has an administrator login who has rights to

update the site, or indeed any forms which can be used to submit content to the

site — even a comment form — read on.



Warning



This article will show you how you can hack in to vulnerable websites, and to

check your own website for one specific vulnerability. It's OK to play around

with this on your own site (but be careful!) but do not be tempted to try it out

on a site you do not own. If the site is properly managed, an attempt to log in

using this or similar methods will be detected and you might find yourself

facing charges under the Computer Misuse Act. Penalties under this act are

severe, including heavy fines or even imprisonment.



What is SQL Injection?



SQL stands for Structured Query Language, and it is the language used by most

website databases. SQL Injection is a technique used by hackers to add their own

SQL to your site's SQL to gain access to confidential information or to change

or delete the data that keeps your website running. I'm going to talk about just

one form of SQL Injection attack that allows a hacker to log in as an

administrator - even if he doesn't know the password.



Is your site vulnerable?



If your website has a login form for an administrator to log in, go to your site

now, in the username field type the administrator user name.



In the password field, type or paste this:



x' or 'a' = 'a



If the website didn't let you log in using this string you can relax a bit; this

article probably doesn't apply to you. However you might like to try this

alternative:



x' or 1=1--



Or you could try pasting either or both of the above strings into both the login

and password field. Or if you are familiar with SQL you could try a few other

variations. A hacker who really wants to get access to your site will try many

variations before he gives up.



If you were able to log in using any of these methods then get your web tech to

read this article, and to read up all the other methods of SQL Injection. The

hackers and "skript kiddies" know all this stuff; your web techs need to know it

too.



The technical stuff



If you were able to log in, then the code which generates the SQL for the login

looks something like this:



$sql =

"SELECT * FROM users

"WHERE username = '" . $username .

"' AND password = '" . $password . "'";



When you log in normally, let's say using userid admin and password secret, what

happens is the admin is put in place of

$username

and secret is put in place of

$password

. The SQL that is generated then looks like this:



SELECT * FROM users WHERE username = 'admin' and PASSWORD = 'secret'



But when you enter

x' or 'a' = 'a

as the password, the SQL which is generated looks like this:



SELECT * FROM users WHERE username = 'admin' and PASSWORD = 'x' or 'a' = 'a'



Notice that the string:

x' or 'a' = 'a

has injected an extra phrase into the WHERE clause:

or 'a' = 'a'

. This means that the WHERE is always true, and so this query will return a row

contain the user's details.



If there is only a single user defined in the database, then that user's details

will always be returned and the system will allow you to log in. If you have

multiple users, then one of those users will be returned at random. If you are

lucky, it will be a user without administration rights (although it might be a

user who has paid to access the site). Do you feel lucky?



How to defend against this type of attack



Fixing this security hole isn't difficult. There are several ways to do it. If

you are using MySQL, for example, the simplest method is to escape the username

and password, using the mysql_escape_string() or mysql_real_escape_string()

functions, e.g.:



$userid = mysql_real_escape_string($userid);

$password = mysql_real_escape_string($password);

$sql =

"SELECT * FROM users

"WHERE username = '" . $username .

"' AND password = '" . $password . "'";



Now when the SQL is built, it will come out as:



SELECT * FROM users WHERE username = 'admin' and PASSWORD = 'x\' or \'a\' = \'a'



Those backslashes ( \ ) make the database treat the quote as a normal character

rather than as a delimiter, so the database no longer interprets the SQL as

having an OR in the WHERE clause.



This is just a simplistic example. In practice you will do a bit more than this

as there are many variations on this attack. For example, you might structure

the SQL differently, fetch the user using the user name only and then check

manually that the password matches or make sure you always use bind variables

(the best defence against SQL injection and strongly recommended!). And you

should always escape all incoming data using the appropriate functions from

whatever language your website is written in - not just data that is being used

for login.



There's more



This has just been a brief overview. There are many more hacking techniques than

SQL Injection; there are many more things that can be done just using SQL

Injection. It is possible to directly change data, get access to confidential

information, even delete your whole database — irrespective of whether the

hacker can actually log in — if your website isn't set up correctly.



If you are hungry for more, this detailed article from SecuriTeam explains other

techiques hackers might use, as well as some of the methods hackers use to work

out the structure of your database, the userid of the admin user, gain access to

your system's configuration, etc.



Have a nice weekend!



Derek