Mitigation of SQL Injection Attack using Prepared Statements (Parameterized Queries)

SQL injection is one of the most common and dangerous vulnerabilities that can affect a database-driven application. Attackers can exploit these vulnerabilities by injecting malicious SQL code into input fields which can lead to unauthorized access, data breaches, or even complete loss of data.

In this article, We will discuss how these methods can help safeguard against SQL injection and provide examples of common attack scenarios. 

What is SQL Injection?

• SQL Injection is a type of attack where malicious SQL code is inserted into input fields of an application, allowing the attacker to manipulate the underlying SQL queries executed by the database.
  
• This can lead to unauthorized data access, data corruption and even the complete compromise of the database.
  
• SQL injection exploits vulnerabilities in the application's handling of user input, bypassing authentication mechanisms or altering queries to benefit the attacker.

Terminology

• Validation: Validation is the process of checking if the input meets a set of criteria (such as a string containing no standalone single quotation marks). 
   
• Sanitization: Sanitization is the process of modifying the input to ensure that it is valid (such as doubling single quotes). 
  
• To prevent SQL injection, all inputs used in dynamic SQL should be properly validated, sanitized, and securely handled, avoiding direct concatenation within queries..

Anatomy of an SQL Attack

An SQL attack has the following two parts:

• Research: View the vulnerable parts of the user-end application that connect with the database. 
   
• Attack: Input malicious fields that can morph the query to your own advantage. 

Example1: 

Consider the following piece of code for an authentication form written in Java: 

String query = "SELECT userName, balance FROM accounts" 
    + "WHERE userID=" + request.getParameter("userID") + 
  "and password='" + request.getParameter("Password") + "'";

try
{
    Statement statement = connection.createStatement();
    ResultSet rs = statement.executeQuery(query);
    while (rs.next()) 
    {
        page.addTableRow(rs.getString("userName"), 
                        rs.getFloat("balance"));
    }
} 
catch (SQLException e) 
    {}

Under normal conditions, a user enters his or her userID and password, and this generates the following statement for execution: 

SELECT userName, balance 
FROM accounts 
WHERE userID=512 and password='thisisyoda'

A possible SQL injection attack would exploit the password field to generate a boolean expression which would make the expression evaluate to true for all cases. Imagine setting the userID and password fields as

userID = 1' or '1' = '1
password = 1' or '1' = '1

The SQL statement then becomes

SELECT userName, balance 
FROM accounts 
WHERE userID='1' OR '1'='1' and 
      password='1' OR '1'='1'

The query will return a value because the condition (OR 1=1) is always true. In this way the system has authenticated the user without knowing the username and password.
The vulnerability can be mitigated using a prepared statement to create a parameterized query as follows:

String query = "SELECT userName, balance "+
               "FROM accounts WHERE userID = ? 
                and password = ?";

try {
  PreparedStatement statement = connection.prepareStatement(query);
  statement.setInt(1, request.getParameter("userID")); 
  ResultSet rs = statement.executeQuery();
  while (rs.next()) 
  {
    page.addTableRow(rs.getString("userName"), 
                     rs.getFloat("balance"));
  }
} catch (SQLException e)
       { ... }

If an attacker attempts to give a value to the userID field that is not a simple integer, then statement.setInt() will throw a SQLException error rather than permitting the query to complete.

Example2: 

Consider another type of attack during authentication: 

String query = "SELECT userID, userName, passwordHash"+
               " FROM users WHERE userName = '" 
               + request.getParameter("user") + "'";
int userID = -1;
HashMap userGroups = new HashMap();
try 
{
  Statement statement = connection.createStatement();
  ResultSet rs = statement.executeQuery(query);
  rs.first();
  userID = rs.getInt("userID");
    
  if (!hashOf(request.getParameter("password")).equals(rs.getString("passwordHash"))) 
  {
    throw BadLoginException();
  }

  String userGroupQuery = "SELECT group FROM groupMembership"+
                         " WHERE userID = " + userID;
    
  rs = statement.executeQuery(userGroupQuery);
    
  while (rs.next()) 
  {
    userGroup.put(rs.getString("group"), true);
  }
} 
catch (SQLException e){}
catch (BadLoginException e){}

A normal query would be as follows. 

SELECT userID, userName, passwordHash 
FROM users 
WHERE userName = 'Anannya'

The attacker may inject the following into the userName field. 

Anannya';
INSERT INTO groupMmbership (userID, group) 
VALUES (SELECT userID FROM users
WHERE userName='Anannya', 'Administrator'); --

Due to this, the actual query will change to: 

SELECT userID, userName, passwordHash FROM 
       users WHERE userName = 'Anannya';
INSERT INTO groupMmbership (userID, group) 
VALUES (SELECT userID FROM users 
WHERE userName='Anannya', 'Administrator'); --'

This will cause another SQL statement to get appended to the actual statement, causing the user to get added to the Administrator database. The attack can be mitigated by using a prepared statement with a parameterized query as follows.

String query = "SELECT userID, userName, passwordHash"+
               " FROM users WHERE userName = ?";

try 
{
  PreparedStatement statement = 
         connection.prepareStatement(userLoginQuery);
  statement.setString(1, request.getParameter("user"));
  ResultSet rs = statement.executeQuery();
} 

Example3: 

Consider another example of query vulnerability discussed below:

String query = "INSERT INTO users VALUES(" + 
        request.getParameter("userName") + ");";

A general query will be: 

INSERT INTO users VALUES("Anannya")

Consider if the attacker enters the following query into the userName field: 

"Anannya); DROP TABLE users;"

The query will then change to:  

INSERT INTO users VALUES("Anannya"); DROP TABLE users;

This query completely deletes the users table upon its execution. A workaround here, again, is a prepared statement.

How does using a Prepared Statement in Java help?

A prepared statement "sanitizes" the input. This means it makes sure that whatever the user enters is treated as a string literal in SQL and NOT as a part of the SQL query. It may also escape certain characters and detect/remove malicious code. In other languages such as PHP, filter_input or filter_input_array can be used to sanitize the string.

Conclusion

SQL injection is a serious threat to the security of any application that interacts with a database. Through a combination of validation, sanitization, and the use of prepared statements, developers can protect their systems from these attacks. By understanding the anatomy of an SQL attack and implementing best practices in coding, the risk of SQL injection can be minimized, ensuring a more secure and reliable application.