SQL injection is one of the most riskiest cyberattacks where an attacker can manipulate SQL queries through user input. This gives them unauthorized access to systems and databases, where they can alter, or even delete records. It is important to prevent SQL injection for WordPress websites to ensure integrity and security of records. 

What is SQL Injection?

SQL Injection typically happens when user inputs are directly included in SQL statements without proper handling. For instance, an attacker could submit the following into a login form:

' OR '1'='1

If this input is passed directly into a SQL query like:

"SELECT * FROM wp_users WHERE user_login = '$input'"

 This returns all users, giving the attacker the access to login without needing credentials. 

How to Prevent SQL Injection in WordPress?

WordPress provides built-in mechanisms to safely query the database through the $wpdb class. Below are the best practices:

1. Use $wpdb->prepare()

This is the primary defense against SQL injection in WordPress. It safely prepares the SQL query using placeholders.

Example:

global $wpdb;
$email = $_POST['email'];
$prepared = $wpdb->prepare( "SELECT * FROM {$wpdb->prefix}users WHERE user_email = %s", $email
);
$user = $wpdb->get_row($prepared);
  • %s means the input is treated as a string.
  • %d would be used for integers.

2. Never Concatenate User Input Directly

Avoid building SQL strings using user input. This is a direct path to vulnerabilities.

Unsafe Example:

$sql = "SELECT * FROM wp_users WHERE user_login = '" . $_GET['user'] . "'";

Safe Alternative:

$user_login = sanitize_user($_GET['user']);
$sql = $wpdb->prepare( "SELECT * FROM wp_users WHERE user_login = %s", $user_login
);

3. Sanitize and Validate Inputs

Use appropriate sanitization and validation functions:

  • sanitize_email()
  • sanitize_text_field()
  • intval()

…and others, depending on the input type.

Example:

$email = sanitize_email($_POST['email']);

4. Use WordPress API Functions Instead of Raw SQL

WordPress offers functions like:

  • get_user_by()
  • get_posts()
  • get_page_by_title()

Which are safer and preferred over writing custom SQL.

Example:

$user = get_user_by('email', sanitize_email($_POST['email']));

5. Limit Database Error Exposure

Avoid showing detailed error messages to users, especially on production websites.

In wp-config.php, set the following:

define( 'WP_DEBUG', false );
define( 'WP_DEBUG_LOG', true );
define( 'WP_DEBUG_DISPLAY', false );

Summary

Preventing SQL injection in WordPress involves:

  • Always using $wpdb->prepare() for SQL queries.
  • Avoiding direct inclusion of user input in queries.
  • Using WordPress API functions that handle data securely.
  • Sanitizing and validating all inputs.
  • Disabling error output in production environments.

SQL injection can compromise your site completely, prevention is a critical, non-negotiable security measure.