An SQL injection Attack consists of injecting sql query portions in the back-end database system via the client interface in the web application. The consequence of a successful exploitation of an SQL injection varies from just reading data to modifying data or executing system commands. SQL Injection in PHP remains the number one attack vector, and also the number on reason for DATA COMPROMISES
Data Validation and prepared statements
It is as simple as this the absence of data validation and prepared statements or stored procedures will increase the possibility that your code contain SQL injections. If your application gives the users the possibility to change parameters and those parameters are not verified and inserted in an unprepared statement than your code contain an SQL Injection.
Example 1 :
<?php $pass=$_GET["pass"]; $con = mysql_connect('localhost', 'owasp', 'abc123'); mysql_select_db("owasp_php", $con); $sql="SELECT card FROM users WHERE password = '".$pass."'"; $result = mysql_query($sql); ?>
The most common ways to prevent SQL Injection in PHP are using functions such as addslashes() and mysql_real_escape_string() but those function can always cause SQL Injections in some cases.
you will avoid Sql injection using addslashes() only in the case when you wrap the query string with quotes.The following example would still be vulnerable
<?php $id = addslashes( $_GET['id'] ); $query = 'SELECT title FROM books WHERE id = ' . $id; ?>
mysql_real_escape_string() is a little bit more powerful than addslashes() as it calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a. As with addslashes(), mysql_real_escape_string() will only work if the query string is wrapped in quotes. A string such as the following would still be vulnerable to an SQL injection:
<?php $bid = mysql_real_escape_string( $_GET['id'] ); $query = 'SELECT title FROM books WHERE id = ' . $bid; ?>
the formula for Sql-injection-free code:
Good Data Validation + Prepared Statement
The PHP Data Objects (PDO) extension defines an abstract database interface that offers parameterized queries for prepared statements and stored procedures. It is available from PHP 5. Use of PDO::prepare will provide good SQL injection defenses, with some exceptions
See Reviewing code for Data Validation (in this guide) Reviewing code for Data Validation
See the OWASP ESAPI Project
The OWASP ESAPI project provides a reference implementation of a security API which can assist in providing security controls to an application.