SQL injection, insertion – Security Tips

SQL injection is a code injection technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed. It is an instance of a more general class of vulnerabilities that can occur whenever one programming or scripting language is embedded inside another. SQL injection attacks are also known as SQL insertion attacks.

SQL injection is an attack where malicious code is passed to an SQL Server for execution. The attack can result in unauthorized access to confidential data, or destruction of critical data
Screen Shot : Doing SQL Injection on simple login page

Before you try to read the methods below, realize that this should only be a concern for PHP developers and the like. If you are using a database driven program (e.g. WordPress, Joomla, OSCommerce), then all you need to do is upgrade your programs to the latest version available.
Methods to prevent SQL injection

Escaping
One way to prevent injections is to escape dangerous characters (i.e. backslash, apostrophe and semicolon). In PHP, it is typical to escape the input using the function mysql_real_escape_string before sending the SQL query. Example:
$Uname = mysql_real_escape_string($Uname);
$Pword = mysql_real_escape_string($Pword);
$query = “SELECT * FROM Users where UserName=’$Uname’ and Password=’$Pword'”;
mysql_query($query);

Parameterized statements
A parametrized query uses placeholders for the input, and the parameter values are supplied at execution time.
$params = array($Uname, $Pword);
$sql = ‘INSERT INTO Users (UserName, Password) VALUES (?, ?)';
$query = sqlsrv_query($connection, $sql, $params);

Advanced: In PHP version 5 and above, there are multiple choices for using parameterized statements; the PDO database layer is one of them. There are also vendor-specific methods; for example, MySQL 4.1 + used with the mysqli extension.