SQL Injection Prevention Techniques

In this article, we will learn how SQL injection dangerous for our system and how can we prevent them. So let's first know what is SQL injection?

SQL Injection is one of the oldest code injection technique which attacker generally used to exploit web applications. Like, if an attacker has inserted some vulnerable query as input, then that input may fetch some important data from your database or delete some information or may be the vulnerable query can delete the entire database. Today, SQL Injection is a common problem for exploited web applications. By using this the attacker can violate transactions, they can become an administrator of database, or they can also effect our bank balance. So before prevention techniques, first let's know how the attacker attempts on SQL data.

These are some examples that vulnerable to SQL injection attack

SQL Injection 1=1

Suppose, there is a table in database name 'employee' and 'emp_name' is one of it's field. In front end, there is some search module that select employee data on the basis of employee name. So in the controller, generally we write the query to fetch the searched employee name as -

$query = "SELECT * FROM employee WHERE emp_name = '$emname ' ";

Suppose the attacker goes to this search module in front end and in place of employee name, he has provided the below code in an employee name variable as

 OR '1' = '1'

Then the select query becomes -

 $query = "SELECT * FROM employee WHERE emp_name = ' ' OR '1' = '1' ";

AS '1' = '1' condition always evaluates to true and executed and fetch all the data from employee table. By this way the attacker can fetch all the employee data.

SQL Injection Additional Query

n addition to provide the desired field value, the attacker can append the additional query that can delete or destroy all records. Like the following input can delete all employee records if the attacker has provided the input as -

a%';DROP TABLE employee;

then the select query becomes

$query = "SELECT * FROM employee WHERE emp_name = ' a%';DROP TABLE employee;' ";

and when this query will be executed, it will delete all the employee data.

Blind SQL Injection

In this, the attacker can pass the query in URL parameters if the webpage url allows it, like

http://www.example.com/employeedetail.php?empid=10

This url gets an employee id 10, and can execute the below query and populate that employee data that having employee id 10

$query = "SELECT * FROM employee WHERE empid = '10'; "

A hacker can also append the condition in the requested url and which may result.

http://www.example.com/employeedetail.php?empid=101 OR 1=1

This may fetch all employee information. Similarly hacker can affect any data in the database.

Methods to prevent SQL injection

These are the methods that protect from SQL vulnerabilities-

By using MySQLi

MySQLi is improved version of MySQL. This improved version is built to use with PHP programming language. If you are using MySQL version 4.3 or newer, then it is recommended to use MySQLi Extension.

MySQLi binds the parameter after the select statement. This process results more security by preventing SQL injection attack and increased performance.

$stmt = $dbConnection->prepare('SELECT * FROM employee WHERE emp_name = ?');
$stmt->bind_param('s', $name);
$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
    // do something with $row
}    

By using PDO

PDO extends for PHP Data Object. It is lightweight, more portable interface for accessing database in PHP. It is a database access layer which makes the developer to write portable code much easier.

In PDO, you can bind the parameter after select statement. The bindparam() method binds a parameter to the specified variable name to fetch the desired value, i.e. it sets the where clause condition and fetch() method fetches a row from the result set. This process protects from SQL injection attack.

$emp_select = $database->prepare("SELECT * FROM employee WHERE emp_name = :empname ");
$emp_select->bindparam(':empname', '$empname');
$emp_select->execute();
$emprows = $emp_select->fetch(PDO::FETCH_ASSOC);
return $emprows;